From: Denis Mukhin <dmukhin@ford.com>
Introduce a driver framework to abstract UART emulators in the hypervisor.
That allows for architecture-independent handling of virtual UARTs in the
console driver and simplifies enabling new UART emulators.
The framework is built under CONFIG_VUART_FRAMEWORK, which will be
automatically enabled once the user enables any UART emulator.
Current implementation supports maximum of one vUART of each kind per domain.
Use new domain_has_vuart() in the console driver code to check whether to
forward console input to the domain using vUART.
Enable console forwarding over vUART for hardware domains with a vUART. That
enables console forwarding to dom0 on x86, since console can be forwarded only
to Xen, dom0 and pvshim on x86 as of now.
Note: existing vUARTs are deliberately *not* hooked to the new framework to
minimize the scope of the patch: vpl011 (i.e. SBSA) emulator and "vuart" (i.e.
minimalistic MMIO-mapped dtuart for hwdoms on Arm) are kept unmodified.
No functional changes for non-x86 architectures.
Signed-off-by: Denis Mukhin <dmukhin@ford.com>
---
Changes since v6:
- addresses Mykola's feedback
- some renaming (vuart_find_by_flags())
- added extra checks to put_rx and dump_state
- fixed vuart_init() error path
- simplified some checks during vUART state 'search'
---
xen/arch/arm/xen.lds.S | 1 +
xen/arch/ppc/xen.lds.S | 1 +
xen/arch/riscv/xen.lds.S | 1 +
xen/arch/x86/xen.lds.S | 1 +
xen/common/Kconfig | 2 +
xen/common/Makefile | 1 +
xen/common/emul/Kconfig | 6 ++
xen/common/emul/Makefile | 1 +
xen/common/emul/vuart/Kconfig | 6 ++
xen/common/emul/vuart/Makefile | 1 +
xen/common/emul/vuart/vuart.c | 165 +++++++++++++++++++++++++++++++++
xen/common/keyhandler.c | 3 +
xen/drivers/char/console.c | 6 +-
xen/include/xen/sched.h | 4 +
xen/include/xen/serial.h | 3 +
xen/include/xen/vuart.h | 115 +++++++++++++++++++++++
xen/include/xen/xen.lds.h | 10 ++
17 files changed, 326 insertions(+), 1 deletion(-)
create mode 100644 xen/common/emul/Kconfig
create mode 100644 xen/common/emul/Makefile
create mode 100644 xen/common/emul/vuart/Kconfig
create mode 100644 xen/common/emul/vuart/Makefile
create mode 100644 xen/common/emul/vuart/vuart.c
create mode 100644 xen/include/xen/vuart.h
diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
index db17ff1efa98..cd05b18770f4 100644
--- a/xen/arch/arm/xen.lds.S
+++ b/xen/arch/arm/xen.lds.S
@@ -58,6 +58,7 @@ SECTIONS
*(.rodata)
*(.rodata.*)
VPCI_ARRAY
+ VUART_ARRAY
*(.data.rel.ro)
*(.data.rel.ro.*)
diff --git a/xen/arch/ppc/xen.lds.S b/xen/arch/ppc/xen.lds.S
index 1de0b77fc6b9..f9d4e5b0dcd8 100644
--- a/xen/arch/ppc/xen.lds.S
+++ b/xen/arch/ppc/xen.lds.S
@@ -52,6 +52,7 @@ SECTIONS
*(.rodata)
*(.rodata.*)
VPCI_ARRAY
+ VUART_ARRAY
*(.data.rel.ro)
*(.data.rel.ro.*)
diff --git a/xen/arch/riscv/xen.lds.S b/xen/arch/riscv/xen.lds.S
index edcadff90bfe..59dcaa5fef9a 100644
--- a/xen/arch/riscv/xen.lds.S
+++ b/xen/arch/riscv/xen.lds.S
@@ -47,6 +47,7 @@ SECTIONS
*(.rodata)
*(.rodata.*)
VPCI_ARRAY
+ VUART_ARRAY
*(.data.rel.ro)
*(.data.rel.ro.*)
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 966e514f2034..d877b93a6964 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -132,6 +132,7 @@ SECTIONS
*(.rodata)
*(.rodata.*)
VPCI_ARRAY
+ VUART_ARRAY
*(.data.rel.ro)
*(.data.rel.ro.*)
diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index 76f9ce705f7a..78a32b69e2b2 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -676,4 +676,6 @@ config PM_STATS
Enable collection of performance management statistics to aid in
analyzing and tuning power/performance characteristics of the system
+source "common/emul/Kconfig"
+
endmenu
diff --git a/xen/common/Makefile b/xen/common/Makefile
index 0c7d0f5d46e1..8c8462565050 100644
--- a/xen/common/Makefile
+++ b/xen/common/Makefile
@@ -12,6 +12,7 @@ obj-$(CONFIG_DEVICE_TREE_PARSE) += device-tree/
obj-$(CONFIG_IOREQ_SERVER) += dm.o
obj-y += domain.o
obj-y += domid.o
+obj-y += emul/
obj-y += event_2l.o
obj-y += event_channel.o
obj-$(CONFIG_EVTCHN_FIFO) += event_fifo.o
diff --git a/xen/common/emul/Kconfig b/xen/common/emul/Kconfig
new file mode 100644
index 000000000000..7c6764d1756b
--- /dev/null
+++ b/xen/common/emul/Kconfig
@@ -0,0 +1,6 @@
+menu "Domain Emulation Features"
+ visible if EXPERT
+
+source "common/emul/vuart/Kconfig"
+
+endmenu
diff --git a/xen/common/emul/Makefile b/xen/common/emul/Makefile
new file mode 100644
index 000000000000..ae0b575c3901
--- /dev/null
+++ b/xen/common/emul/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_VUART_FRAMEWORK) += vuart/
diff --git a/xen/common/emul/vuart/Kconfig b/xen/common/emul/vuart/Kconfig
new file mode 100644
index 000000000000..ce1b976b7da7
--- /dev/null
+++ b/xen/common/emul/vuart/Kconfig
@@ -0,0 +1,6 @@
+config VUART_FRAMEWORK
+ bool
+
+menu "UART Emulation"
+
+endmenu
diff --git a/xen/common/emul/vuart/Makefile b/xen/common/emul/vuart/Makefile
new file mode 100644
index 000000000000..97f792dc6641
--- /dev/null
+++ b/xen/common/emul/vuart/Makefile
@@ -0,0 +1 @@
+obj-y += vuart.o
diff --git a/xen/common/emul/vuart/vuart.c b/xen/common/emul/vuart/vuart.c
new file mode 100644
index 000000000000..ba89d608aeb2
--- /dev/null
+++ b/xen/common/emul/vuart/vuart.c
@@ -0,0 +1,165 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * UART emulator framework.
+ *
+ * Copyright 2025 Ford Motor Company
+ */
+
+#include <xen/err.h>
+#include <xen/sched.h>
+#include <xen/vuart.h>
+#include <xen/xvmalloc.h>
+
+#define for_each_emulator(e) \
+ for ( e = vuart_array_start; e < vuart_array_end; e++ )
+
+extern const struct vuart_emulator vuart_array_start[];
+extern const struct vuart_emulator vuart_array_end[];
+
+static const struct vuart_emulator *
+vuart_match_by_compatible(const struct domain *d, const char *compat)
+{
+ const struct vuart_emulator *emulator;
+
+ for_each_emulator(emulator)
+ if ( emulator->compatible &&
+ !strncmp(compat, emulator->compatible,
+ strlen(emulator->compatible)) )
+ return emulator;
+
+ return NULL;
+}
+
+const static struct vuart *
+vuart_find_by_flags(const struct domain *d, unsigned int flags)
+{
+ const struct vuart *vuart = d->console.vuart;
+
+ if ( vuart && (vuart->flags & flags) )
+ return vuart;
+
+ return NULL;
+}
+
+struct vuart *vuart_find_by_io_range(struct domain *d, unsigned long addr,
+ unsigned long size)
+{
+ struct vuart *vuart = d->console.vuart;
+
+ if ( vuart &&
+ addr >= vuart->info->base_addr &&
+ addr + size - 1 <= vuart->info->base_addr + vuart->info->size - 1 )
+ return vuart;
+
+ return NULL;
+}
+
+int vuart_init(struct domain *d, const struct vuart_info *info)
+{
+ const struct vuart_emulator *emulator;
+ struct vuart *vuart;
+ int rc;
+
+ if ( d->console.vuart )
+ return -EBUSY;
+
+ emulator = vuart_match_by_compatible(d, info->compatible);
+ if ( !emulator )
+ return -ENODEV;
+
+ vuart = xzalloc(typeof(*vuart));
+ if ( !vuart )
+ return -ENOMEM;
+
+ vuart->info = xvzalloc(typeof(*vuart->info));
+ if ( !vuart->info )
+ {
+ rc = -ENOMEM;
+ goto err_out1;
+ }
+ memcpy(vuart->info, info, sizeof(*info));
+
+ vuart->vdev = emulator->alloc(d, vuart->info);
+ if ( IS_ERR(vuart->vdev) )
+ {
+ rc = PTR_ERR(vuart->vdev);
+ goto err_out2;
+ }
+
+ vuart->emulator = emulator;
+ vuart->owner = d;
+ vuart->flags |= VUART_CONSOLE_INPUT;
+
+ d->console.input_allowed = true;
+ d->console.vuart = vuart;
+
+ return 0;
+
+ err_out2:
+ xvfree(vuart->info);
+ err_out1:
+ xvfree(vuart);
+
+ return rc;
+}
+
+/*
+ * Release any resources taken by UART emulators.
+ *
+ * NB: no flags are cleared, since currently exit() is called only during
+ * domain destroy.
+ */
+void vuart_deinit(struct domain *d)
+{
+ struct vuart *vuart = d->console.vuart;
+
+ if ( vuart )
+ {
+ vuart->emulator->free(vuart->vdev);
+ xvfree(vuart->info);
+ }
+ XVFREE(d->console.vuart);
+}
+
+/*
+ * Print emulated UART state on the console.
+ *
+ * Must be called under rcu_lock_domain().
+ */
+void vuart_dump_state(const struct domain *d)
+{
+ struct vuart *vuart = d->console.vuart;
+
+ if ( vuart && vuart->emulator->dump_state )
+ vuart->emulator->dump_state(vuart->vdev);
+}
+
+/*
+ * Put character to the first emulated UART's FIFO with the physical console
+ * forwarding enabled.
+ *
+ * Must be called under rcu_lock_domain().
+ */
+int vuart_put_rx(struct domain *d, char c)
+{
+ const struct vuart *vuart = vuart_find_by_flags(d, VUART_CONSOLE_INPUT);
+
+ if ( vuart && vuart->emulator->put_rx )
+ return vuart->emulator->put_rx(vuart->vdev, c);
+
+ return -ENODEV;
+}
+
+bool domain_has_vuart(const struct domain *d)
+{
+ return vuart_find_by_flags(d, VUART_CONSOLE_INPUT);
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/common/keyhandler.c b/xen/common/keyhandler.c
index cb6df2823b00..156e64d9eb58 100644
--- a/xen/common/keyhandler.c
+++ b/xen/common/keyhandler.c
@@ -22,6 +22,7 @@
#include <xen/mm.h>
#include <xen/watchdog.h>
#include <xen/init.h>
+#include <xen/vuart.h>
#include <asm/div64.h>
static unsigned char keypress_key;
@@ -352,6 +353,8 @@ static void cf_check dump_domains(unsigned char key)
v->periodic_period / 1000000);
}
}
+
+ vuart_dump_state(d);
}
for_each_domain ( d )
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 9bd5b4825da6..d5164897a776 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -33,6 +33,7 @@
#include <asm/setup.h>
#include <xen/sections.h>
#include <xen/consoled.h>
+#include <xen/vuart.h>
#ifdef CONFIG_X86
#include <asm/guest.h>
@@ -596,11 +597,12 @@ static void __serial_rx(char c)
if ( !d )
return;
- if ( is_hardware_domain(d) )
+ if ( is_hardware_domain(d) && !domain_has_vuart(d) )
{
/*
* Deliver input to the hardware domain buffer, unless it is
* already full.
+ * NB: must be the first check: hardware domain may have emulated UART.
*/
if ( (serial_rx_prod - serial_rx_cons) != SERIAL_RX_SIZE )
serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
@@ -611,6 +613,8 @@ static void __serial_rx(char c)
*/
send_global_virq(VIRQ_CONSOLE);
}
+ else if ( domain_has_vuart(d) )
+ rc = vuart_put_rx(d, c);
#ifdef CONFIG_SBSA_VUART_CONSOLE
else
/* Deliver input to the emulated UART. */
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 02bdc256ce37..613f4596e33d 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -23,6 +23,7 @@
#include <asm/atomic.h>
#include <asm/current.h>
#include <xen/vpci.h>
+#include <xen/vuart.h>
#include <xen/wait.h>
#include <public/xen.h>
#include <public/domctl.h>
@@ -660,6 +661,9 @@ struct domain
struct {
/* Permission to take ownership of the physical console input. */
bool input_allowed;
+#ifdef CONFIG_VUART_FRAMEWORK
+ struct vuart *vuart;
+#endif
} console;
} __aligned(PAGE_SIZE);
diff --git a/xen/include/xen/serial.h b/xen/include/xen/serial.h
index 8e1844555208..123eee67df35 100644
--- a/xen/include/xen/serial.h
+++ b/xen/include/xen/serial.h
@@ -36,6 +36,9 @@ struct vuart_info {
unsigned long data_off; /* Data register offset */
unsigned long status_off; /* Status register offset */
unsigned long status; /* Ready status value */
+ unsigned int irq; /* Interrupt */
+ char compatible[16]; /* Compatible string */
+ char name[16]; /* User-friendly name */
};
struct serial_port {
diff --git a/xen/include/xen/vuart.h b/xen/include/xen/vuart.h
new file mode 100644
index 000000000000..55828f8498ce
--- /dev/null
+++ b/xen/include/xen/vuart.h
@@ -0,0 +1,115 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * UART emulator framework.
+ *
+ * Copyright 2025 Ford Motor Company
+ */
+
+#ifndef XEN_VUART_H
+#define XEN_VUART_H
+
+#include <xen/serial.h>
+#include <public/xen.h>
+
+struct vuart_emulator;
+
+enum {
+ VUART_CONSOLE_INPUT = BIT(0, U), /* Physical console input forwarding. */
+};
+
+/*
+ * FIXME: #ifdef is temporary to avoid clash with
+ * arch/arm/include/asm/domain.h
+ */
+#ifdef CONFIG_VUART_FRAMEWORK
+struct vuart {
+ const struct vuart_emulator *emulator;
+ struct vuart_info *info;
+ struct domain *owner;
+ unsigned int flags;
+ void *vdev;
+};
+#endif
+
+struct vuart_emulator {
+ /* UART compatible string. Cannot be NULL or empty. */
+ const char *compatible;
+
+ /*
+ * Allocate emulated UART state (RX/TX FIFOs, locks, initialize registers,
+ * hook I/O handlers, etc.)
+ * Cannot be NULL.
+ */
+ void *(*alloc)(struct domain *d, const struct vuart_info *info);
+
+ /*
+ * Release resources used to emulate UART state (flush RX/TX FIFOs, unhook
+ * I/O handlers, etc.).
+ * Cannot be NULL.
+ */
+ void (*free)(void *arg);
+
+ /*
+ * Print emulated UART state, including registers, on the console.
+ * Can be NULL.
+ */
+ void (*dump_state)(void *arg);
+
+ /*
+ * Place character to the emulated RX FIFO.
+ * Used to forward physical console input to the guest OS.
+ * Can be NULL.
+ */
+ int (*put_rx)(void *arg, char c);
+};
+
+#define VUART_REGISTER(name, x) \
+ static const struct vuart_emulator name##_entry \
+ __used_section(".data.rel.ro.vuart") = x
+
+struct vuart *vuart_find_by_io_range(struct domain *d,
+ unsigned long base_addr,
+ unsigned long size);
+
+int vuart_put_rx(struct domain *d, char c);
+
+#ifdef CONFIG_VUART_FRAMEWORK
+
+int vuart_init(struct domain *d, const struct vuart_info *info);
+void vuart_deinit(struct domain *d);
+void vuart_dump_state(const struct domain *d);
+bool domain_has_vuart(const struct domain *d);
+
+#else
+
+static inline int vuart_init(struct domain *d, const struct vuart_info *info)
+{
+ return 0;
+}
+
+static inline void vuart_deinit(struct domain *d)
+{
+}
+
+static inline void vuart_dump_state(const struct domain *d)
+{
+}
+
+static inline bool domain_has_vuart(const struct domain *d)
+{
+ return false;
+}
+
+#endif /* CONFIG_VUART_FRAMEWORK */
+
+#endif /* XEN_VUART_H */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
+
diff --git a/xen/include/xen/xen.lds.h b/xen/include/xen/xen.lds.h
index b126dfe88792..2d65f32ddad3 100644
--- a/xen/include/xen/xen.lds.h
+++ b/xen/include/xen/xen.lds.h
@@ -194,4 +194,14 @@
#define VPCI_ARRAY
#endif
+#ifdef CONFIG_VUART_FRAMEWORK
+#define VUART_ARRAY \
+ . = ALIGN(POINTER_ALIGN); \
+ vuart_array_start = .; \
+ *(.data.rel.ro.vuart) \
+ vuart_array_end = .;
+#else
+#define VUART_ARRAY
+#endif
+
#endif /* __XEN_LDS_H__ */
--
2.51.0Hi Denis,
Thank you for addressing the issues from the previous version of the
patch series,
Everything looks good to me, with just a few questions:
On Tue, Sep 9, 2025 at 12:56 AM <dmukhin@xen.org> wrote:
>
> From: Denis Mukhin <dmukhin@ford.com>
>
> Introduce a driver framework to abstract UART emulators in the hypervisor.
>
> That allows for architecture-independent handling of virtual UARTs in the
> console driver and simplifies enabling new UART emulators.
>
> The framework is built under CONFIG_VUART_FRAMEWORK, which will be
> automatically enabled once the user enables any UART emulator.
>
> Current implementation supports maximum of one vUART of each kind per domain.
>
> Use new domain_has_vuart() in the console driver code to check whether to
> forward console input to the domain using vUART.
>
> Enable console forwarding over vUART for hardware domains with a vUART. That
> enables console forwarding to dom0 on x86, since console can be forwarded only
> to Xen, dom0 and pvshim on x86 as of now.
>
> Note: existing vUARTs are deliberately *not* hooked to the new framework to
> minimize the scope of the patch: vpl011 (i.e. SBSA) emulator and "vuart" (i.e.
> minimalistic MMIO-mapped dtuart for hwdoms on Arm) are kept unmodified.
>
> No functional changes for non-x86 architectures.
>
> Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> ---
> Changes since v6:
> - addresses Mykola's feedback
> - some renaming (vuart_find_by_flags())
> - added extra checks to put_rx and dump_state
> - fixed vuart_init() error path
> - simplified some checks during vUART state 'search'
> ---
> xen/arch/arm/xen.lds.S | 1 +
> xen/arch/ppc/xen.lds.S | 1 +
> xen/arch/riscv/xen.lds.S | 1 +
> xen/arch/x86/xen.lds.S | 1 +
> xen/common/Kconfig | 2 +
> xen/common/Makefile | 1 +
> xen/common/emul/Kconfig | 6 ++
> xen/common/emul/Makefile | 1 +
> xen/common/emul/vuart/Kconfig | 6 ++
> xen/common/emul/vuart/Makefile | 1 +
> xen/common/emul/vuart/vuart.c | 165 +++++++++++++++++++++++++++++++++
> xen/common/keyhandler.c | 3 +
> xen/drivers/char/console.c | 6 +-
> xen/include/xen/sched.h | 4 +
> xen/include/xen/serial.h | 3 +
> xen/include/xen/vuart.h | 115 +++++++++++++++++++++++
> xen/include/xen/xen.lds.h | 10 ++
> 17 files changed, 326 insertions(+), 1 deletion(-)
> create mode 100644 xen/common/emul/Kconfig
> create mode 100644 xen/common/emul/Makefile
> create mode 100644 xen/common/emul/vuart/Kconfig
> create mode 100644 xen/common/emul/vuart/Makefile
> create mode 100644 xen/common/emul/vuart/vuart.c
> create mode 100644 xen/include/xen/vuart.h
>
> diff --git a/xen/arch/arm/xen.lds.S b/xen/arch/arm/xen.lds.S
> index db17ff1efa98..cd05b18770f4 100644
> --- a/xen/arch/arm/xen.lds.S
> +++ b/xen/arch/arm/xen.lds.S
> @@ -58,6 +58,7 @@ SECTIONS
> *(.rodata)
> *(.rodata.*)
> VPCI_ARRAY
> + VUART_ARRAY
> *(.data.rel.ro)
> *(.data.rel.ro.*)
>
> diff --git a/xen/arch/ppc/xen.lds.S b/xen/arch/ppc/xen.lds.S
> index 1de0b77fc6b9..f9d4e5b0dcd8 100644
> --- a/xen/arch/ppc/xen.lds.S
> +++ b/xen/arch/ppc/xen.lds.S
> @@ -52,6 +52,7 @@ SECTIONS
> *(.rodata)
> *(.rodata.*)
> VPCI_ARRAY
> + VUART_ARRAY
> *(.data.rel.ro)
> *(.data.rel.ro.*)
>
> diff --git a/xen/arch/riscv/xen.lds.S b/xen/arch/riscv/xen.lds.S
> index edcadff90bfe..59dcaa5fef9a 100644
> --- a/xen/arch/riscv/xen.lds.S
> +++ b/xen/arch/riscv/xen.lds.S
> @@ -47,6 +47,7 @@ SECTIONS
> *(.rodata)
> *(.rodata.*)
> VPCI_ARRAY
> + VUART_ARRAY
> *(.data.rel.ro)
> *(.data.rel.ro.*)
>
> diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
> index 966e514f2034..d877b93a6964 100644
> --- a/xen/arch/x86/xen.lds.S
> +++ b/xen/arch/x86/xen.lds.S
> @@ -132,6 +132,7 @@ SECTIONS
> *(.rodata)
> *(.rodata.*)
> VPCI_ARRAY
> + VUART_ARRAY
> *(.data.rel.ro)
> *(.data.rel.ro.*)
>
> diff --git a/xen/common/Kconfig b/xen/common/Kconfig
> index 76f9ce705f7a..78a32b69e2b2 100644
> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -676,4 +676,6 @@ config PM_STATS
> Enable collection of performance management statistics to aid in
> analyzing and tuning power/performance characteristics of the system
>
> +source "common/emul/Kconfig"
> +
> endmenu
> diff --git a/xen/common/Makefile b/xen/common/Makefile
> index 0c7d0f5d46e1..8c8462565050 100644
> --- a/xen/common/Makefile
> +++ b/xen/common/Makefile
> @@ -12,6 +12,7 @@ obj-$(CONFIG_DEVICE_TREE_PARSE) += device-tree/
> obj-$(CONFIG_IOREQ_SERVER) += dm.o
> obj-y += domain.o
> obj-y += domid.o
> +obj-y += emul/
> obj-y += event_2l.o
> obj-y += event_channel.o
> obj-$(CONFIG_EVTCHN_FIFO) += event_fifo.o
> diff --git a/xen/common/emul/Kconfig b/xen/common/emul/Kconfig
> new file mode 100644
> index 000000000000..7c6764d1756b
> --- /dev/null
> +++ b/xen/common/emul/Kconfig
> @@ -0,0 +1,6 @@
> +menu "Domain Emulation Features"
> + visible if EXPERT
> +
> +source "common/emul/vuart/Kconfig"
> +
> +endmenu
> diff --git a/xen/common/emul/Makefile b/xen/common/emul/Makefile
> new file mode 100644
> index 000000000000..ae0b575c3901
> --- /dev/null
> +++ b/xen/common/emul/Makefile
> @@ -0,0 +1 @@
> +obj-$(CONFIG_VUART_FRAMEWORK) += vuart/
> diff --git a/xen/common/emul/vuart/Kconfig b/xen/common/emul/vuart/Kconfig
> new file mode 100644
> index 000000000000..ce1b976b7da7
> --- /dev/null
> +++ b/xen/common/emul/vuart/Kconfig
> @@ -0,0 +1,6 @@
> +config VUART_FRAMEWORK
> + bool
> +
> +menu "UART Emulation"
> +
> +endmenu
> diff --git a/xen/common/emul/vuart/Makefile b/xen/common/emul/vuart/Makefile
> new file mode 100644
> index 000000000000..97f792dc6641
> --- /dev/null
> +++ b/xen/common/emul/vuart/Makefile
> @@ -0,0 +1 @@
> +obj-y += vuart.o
> diff --git a/xen/common/emul/vuart/vuart.c b/xen/common/emul/vuart/vuart.c
> new file mode 100644
> index 000000000000..ba89d608aeb2
> --- /dev/null
> +++ b/xen/common/emul/vuart/vuart.c
> @@ -0,0 +1,165 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * UART emulator framework.
> + *
> + * Copyright 2025 Ford Motor Company
> + */
> +
> +#include <xen/err.h>
> +#include <xen/sched.h>
> +#include <xen/vuart.h>
> +#include <xen/xvmalloc.h>
> +
> +#define for_each_emulator(e) \
> + for ( e = vuart_array_start; e < vuart_array_end; e++ )
> +
> +extern const struct vuart_emulator vuart_array_start[];
> +extern const struct vuart_emulator vuart_array_end[];
> +
> +static const struct vuart_emulator *
> +vuart_match_by_compatible(const struct domain *d, const char *compat)
> +{
> + const struct vuart_emulator *emulator;
> +
> + for_each_emulator(emulator)
> + if ( emulator->compatible &&
> + !strncmp(compat, emulator->compatible,
> + strlen(emulator->compatible)) )
> + return emulator;
> +
> + return NULL;
> +}
> +
> +const static struct vuart *
> +vuart_find_by_flags(const struct domain *d, unsigned int flags)
> +{
> + const struct vuart *vuart = d->console.vuart;
> +
> + if ( vuart && (vuart->flags & flags) )
> + return vuart;
> +
> + return NULL;
> +}
> +
> +struct vuart *vuart_find_by_io_range(struct domain *d, unsigned long addr,
> + unsigned long size)
> +{
> + struct vuart *vuart = d->console.vuart;
> +
> + if ( vuart &&
> + addr >= vuart->info->base_addr &&
> + addr + size - 1 <= vuart->info->base_addr + vuart->info->size - 1 )
> + return vuart;
> +
> + return NULL;
> +}
> +
> +int vuart_init(struct domain *d, const struct vuart_info *info)
> +{
> + const struct vuart_emulator *emulator;
> + struct vuart *vuart;
> + int rc;
> +
> + if ( d->console.vuart )
> + return -EBUSY;
> +
> + emulator = vuart_match_by_compatible(d, info->compatible);
> + if ( !emulator )
> + return -ENODEV;
> +
> + vuart = xzalloc(typeof(*vuart));
> + if ( !vuart )
> + return -ENOMEM;
> +
> + vuart->info = xvzalloc(typeof(*vuart->info));
> + if ( !vuart->info )
> + {
> + rc = -ENOMEM;
> + goto err_out1;
> + }
> + memcpy(vuart->info, info, sizeof(*info));
> +
> + vuart->vdev = emulator->alloc(d, vuart->info);
> + if ( IS_ERR(vuart->vdev) )
> + {
> + rc = PTR_ERR(vuart->vdev);
> + goto err_out2;
> + }
> +
> + vuart->emulator = emulator;
> + vuart->owner = d;
> + vuart->flags |= VUART_CONSOLE_INPUT;
> +
> + d->console.input_allowed = true;
I'm not a specialist in the area of consoles, but I'm wondering:
Does the input_allowed flag serve the same purpose as
VUART_CONSOLE_INPUT? If so, do we need both, or
could one be removed to simplify the code?
At least here they are set in sync.
> + d->console.vuart = vuart;
> +
> + return 0;
> +
> + err_out2:
> + xvfree(vuart->info);
> + err_out1:
> + xvfree(vuart);
> +
> + return rc;
> +}
> +
> +/*
> + * Release any resources taken by UART emulators.
> + *
> + * NB: no flags are cleared, since currently exit() is called only during
> + * domain destroy.
> + */
> +void vuart_deinit(struct domain *d)
> +{
> + struct vuart *vuart = d->console.vuart;
> +
> + if ( vuart )
> + {
> + vuart->emulator->free(vuart->vdev);
> + xvfree(vuart->info);
> + }
> + XVFREE(d->console.vuart);
> +}
> +
> +/*
> + * Print emulated UART state on the console.
> + *
> + * Must be called under rcu_lock_domain().
> + */
> +void vuart_dump_state(const struct domain *d)
> +{
> + struct vuart *vuart = d->console.vuart;
> +
> + if ( vuart && vuart->emulator->dump_state )
> + vuart->emulator->dump_state(vuart->vdev);
> +}
> +
> +/*
> + * Put character to the first emulated UART's FIFO with the physical console
> + * forwarding enabled.
> + *
> + * Must be called under rcu_lock_domain().
> + */
> +int vuart_put_rx(struct domain *d, char c)
> +{
> + const struct vuart *vuart = vuart_find_by_flags(d, VUART_CONSOLE_INPUT);
The call to vuart_find_by_flags() with VUART_CONSOLE_INPUT in
vuart_put_rx() appears unnecessary. Every vUART console is always
initialized with VUART_CONSOLE_INPUT, so even if multiple consoles
exist, the search will always return the first console. It would be
simpler and clearer to use d->console.vuart directly.
Consider updating the function to remove the flag-based search and add a
short comment explaining why checking the flag isn’t needed. This will
help avoid confusion for future maintainers. Alternatively, we could
pass flags to the init functions instead of hardcoding
VUART_CONSOLE_INPUT for every console.
> +
> + if ( vuart && vuart->emulator->put_rx )
> + return vuart->emulator->put_rx(vuart->vdev, c);
> +
> + return -ENODEV;
> +}
> +
> +bool domain_has_vuart(const struct domain *d)
> +{
> + return vuart_find_by_flags(d, VUART_CONSOLE_INPUT);
The same issue applies here: domain_has_vuart() calls
vuart_find_by_flags() with VUART_CONSOLE_INPUT, but every
vUART console is always initialized with this flag
> +}
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> diff --git a/xen/common/keyhandler.c b/xen/common/keyhandler.c
> index cb6df2823b00..156e64d9eb58 100644
> --- a/xen/common/keyhandler.c
> +++ b/xen/common/keyhandler.c
> @@ -22,6 +22,7 @@
> #include <xen/mm.h>
> #include <xen/watchdog.h>
> #include <xen/init.h>
> +#include <xen/vuart.h>
> #include <asm/div64.h>
>
> static unsigned char keypress_key;
> @@ -352,6 +353,8 @@ static void cf_check dump_domains(unsigned char key)
> v->periodic_period / 1000000);
> }
> }
> +
> + vuart_dump_state(d);
> }
>
> for_each_domain ( d )
> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> index 9bd5b4825da6..d5164897a776 100644
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -33,6 +33,7 @@
> #include <asm/setup.h>
> #include <xen/sections.h>
> #include <xen/consoled.h>
> +#include <xen/vuart.h>
>
> #ifdef CONFIG_X86
> #include <asm/guest.h>
> @@ -596,11 +597,12 @@ static void __serial_rx(char c)
> if ( !d )
> return;
>
> - if ( is_hardware_domain(d) )
> + if ( is_hardware_domain(d) && !domain_has_vuart(d) )
> {
> /*
> * Deliver input to the hardware domain buffer, unless it is
> * already full.
> + * NB: must be the first check: hardware domain may have emulated UART.
> */
> if ( (serial_rx_prod - serial_rx_cons) != SERIAL_RX_SIZE )
> serial_rx_ring[SERIAL_RX_MASK(serial_rx_prod++)] = c;
> @@ -611,6 +613,8 @@ static void __serial_rx(char c)
> */
> send_global_virq(VIRQ_CONSOLE);
> }
> + else if ( domain_has_vuart(d) )
> + rc = vuart_put_rx(d, c);
> #ifdef CONFIG_SBSA_VUART_CONSOLE
> else
> /* Deliver input to the emulated UART. */
> diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
> index 02bdc256ce37..613f4596e33d 100644
> --- a/xen/include/xen/sched.h
> +++ b/xen/include/xen/sched.h
> @@ -23,6 +23,7 @@
> #include <asm/atomic.h>
> #include <asm/current.h>
> #include <xen/vpci.h>
> +#include <xen/vuart.h>
> #include <xen/wait.h>
> #include <public/xen.h>
> #include <public/domctl.h>
> @@ -660,6 +661,9 @@ struct domain
> struct {
> /* Permission to take ownership of the physical console input. */
> bool input_allowed;
> +#ifdef CONFIG_VUART_FRAMEWORK
> + struct vuart *vuart;
> +#endif
> } console;
> } __aligned(PAGE_SIZE);
>
> diff --git a/xen/include/xen/serial.h b/xen/include/xen/serial.h
> index 8e1844555208..123eee67df35 100644
> --- a/xen/include/xen/serial.h
> +++ b/xen/include/xen/serial.h
> @@ -36,6 +36,9 @@ struct vuart_info {
> unsigned long data_off; /* Data register offset */
> unsigned long status_off; /* Status register offset */
> unsigned long status; /* Ready status value */
> + unsigned int irq; /* Interrupt */
> + char compatible[16]; /* Compatible string */
> + char name[16]; /* User-friendly name */
> };
>
> struct serial_port {
> diff --git a/xen/include/xen/vuart.h b/xen/include/xen/vuart.h
> new file mode 100644
> index 000000000000..55828f8498ce
> --- /dev/null
> +++ b/xen/include/xen/vuart.h
> @@ -0,0 +1,115 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * UART emulator framework.
> + *
> + * Copyright 2025 Ford Motor Company
> + */
> +
> +#ifndef XEN_VUART_H
> +#define XEN_VUART_H
> +
> +#include <xen/serial.h>
> +#include <public/xen.h>
> +
> +struct vuart_emulator;
> +
> +enum {
> + VUART_CONSOLE_INPUT = BIT(0, U), /* Physical console input forwarding. */
> +};
> +
> +/*
> + * FIXME: #ifdef is temporary to avoid clash with
> + * arch/arm/include/asm/domain.h
> + */
> +#ifdef CONFIG_VUART_FRAMEWORK
> +struct vuart {
> + const struct vuart_emulator *emulator;
> + struct vuart_info *info;
> + struct domain *owner;
> + unsigned int flags;
> + void *vdev;
> +};
> +#endif
> +
> +struct vuart_emulator {
> + /* UART compatible string. Cannot be NULL or empty. */
> + const char *compatible;
> +
> + /*
> + * Allocate emulated UART state (RX/TX FIFOs, locks, initialize registers,
> + * hook I/O handlers, etc.)
> + * Cannot be NULL.
> + */
> + void *(*alloc)(struct domain *d, const struct vuart_info *info);
> +
> + /*
> + * Release resources used to emulate UART state (flush RX/TX FIFOs, unhook
> + * I/O handlers, etc.).
> + * Cannot be NULL.
> + */
> + void (*free)(void *arg);
> +
> + /*
> + * Print emulated UART state, including registers, on the console.
> + * Can be NULL.
> + */
> + void (*dump_state)(void *arg);
> +
> + /*
> + * Place character to the emulated RX FIFO.
> + * Used to forward physical console input to the guest OS.
> + * Can be NULL.
> + */
> + int (*put_rx)(void *arg, char c);
> +};
> +
> +#define VUART_REGISTER(name, x) \
> + static const struct vuart_emulator name##_entry \
> + __used_section(".data.rel.ro.vuart") = x
> +
> +struct vuart *vuart_find_by_io_range(struct domain *d,
> + unsigned long base_addr,
> + unsigned long size);
> +
> +int vuart_put_rx(struct domain *d, char c);
> +
> +#ifdef CONFIG_VUART_FRAMEWORK
> +
> +int vuart_init(struct domain *d, const struct vuart_info *info);
> +void vuart_deinit(struct domain *d);
> +void vuart_dump_state(const struct domain *d);
> +bool domain_has_vuart(const struct domain *d);
> +
> +#else
> +
> +static inline int vuart_init(struct domain *d, const struct vuart_info *info)
> +{
> + return 0;
> +}
> +
> +static inline void vuart_deinit(struct domain *d)
> +{
> +}
> +
> +static inline void vuart_dump_state(const struct domain *d)
> +{
> +}
> +
> +static inline bool domain_has_vuart(const struct domain *d)
> +{
> + return false;
> +}
> +
> +#endif /* CONFIG_VUART_FRAMEWORK */
> +
> +#endif /* XEN_VUART_H */
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> +
> diff --git a/xen/include/xen/xen.lds.h b/xen/include/xen/xen.lds.h
> index b126dfe88792..2d65f32ddad3 100644
> --- a/xen/include/xen/xen.lds.h
> +++ b/xen/include/xen/xen.lds.h
> @@ -194,4 +194,14 @@
> #define VPCI_ARRAY
> #endif
>
> +#ifdef CONFIG_VUART_FRAMEWORK
> +#define VUART_ARRAY \
> + . = ALIGN(POINTER_ALIGN); \
> + vuart_array_start = .; \
> + *(.data.rel.ro.vuart) \
> + vuart_array_end = .;
> +#else
> +#define VUART_ARRAY
> +#endif
> +
> #endif /* __XEN_LDS_H__ */
> --
> 2.51.0
>
>
Best regards,
Mykola
On Wed, Sep 10, 2025 at 10:57:14AM +0300, Mykola Kvach wrote:
> > +int vuart_init(struct domain *d, const struct vuart_info *info)
> > +{
> > + const struct vuart_emulator *emulator;
> > + struct vuart *vuart;
> > + int rc;
> > +
> > + if ( d->console.vuart )
> > + return -EBUSY;
> > +
> > + emulator = vuart_match_by_compatible(d, info->compatible);
> > + if ( !emulator )
> > + return -ENODEV;
> > +
> > + vuart = xzalloc(typeof(*vuart));
> > + if ( !vuart )
> > + return -ENOMEM;
> > +
> > + vuart->info = xvzalloc(typeof(*vuart->info));
> > + if ( !vuart->info )
> > + {
> > + rc = -ENOMEM;
> > + goto err_out1;
> > + }
> > + memcpy(vuart->info, info, sizeof(*info));
> > +
> > + vuart->vdev = emulator->alloc(d, vuart->info);
> > + if ( IS_ERR(vuart->vdev) )
> > + {
> > + rc = PTR_ERR(vuart->vdev);
> > + goto err_out2;
> > + }
> > +
> > + vuart->emulator = emulator;
> > + vuart->owner = d;
> > + vuart->flags |= VUART_CONSOLE_INPUT;
> > +
> > + d->console.input_allowed = true;
>
> I'm not a specialist in the area of consoles, but I'm wondering:
> Does the input_allowed flag serve the same purpose as
> VUART_CONSOLE_INPUT? If so, do we need both, or
> could one be removed to simplify the code?
At this point these two flags must be in sync.
`console.input_allowed` is a permission for a domain to take the physical
console input.
`VUART_CONSOLE_INPUT` in `vuart->flags` is a permission for vUART to take
the physical console input.
pvshim does not have vUART, but can have console focus.
And not every vUART can be configured to have a console input (e.g. Arm's
"hwdom vuart").
> > +/*
> > + * Put character to the first emulated UART's FIFO with the physical console
> > + * forwarding enabled.
> > + *
> > + * Must be called under rcu_lock_domain().
> > + */
> > +int vuart_put_rx(struct domain *d, char c)
> > +{
> > + const struct vuart *vuart = vuart_find_by_flags(d, VUART_CONSOLE_INPUT);
>
> The call to vuart_find_by_flags() with VUART_CONSOLE_INPUT in
> vuart_put_rx() appears unnecessary. Every vUART console is always
> initialized with VUART_CONSOLE_INPUT, so even if multiple consoles
> exist, the search will always return the first console. It would be
> simpler and clearer to use d->console.vuart directly.
There's no certain order in which multiple vUARTs are initialized, so there
should be something which scans the vUART list and selects the vUART with
console input permission. Follow on Arm's change will add multiple vUARTs
and I decided to generalize logic in this patch, so that there will be
minimal update in vuart_find_by_flags() only.
>
> Consider updating the function to remove the flag-based search and add a
> short comment explaining why checking the flag isn’t needed. This will
> help avoid confusion for future maintainers. Alternatively, we could
> pass flags to the init functions instead of hardcoding
> VUART_CONSOLE_INPUT for every console.
That will work, thanks for suggestion.
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