Enable FRED right after init_mem_mapping() to avoid #PF handler,
exc_page_fault(), fetching its faulting address from the stack
before FRED is enabled.
Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
---
arch/x86/kernel/cpu/common.c | 6 +-----
arch/x86/kernel/setup.c | 11 ++++++++++-
arch/x86/kernel/smpboot.c | 6 ++++++
arch/x86/kernel/traps.c | 4 ++++
4 files changed, 21 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 6de12b3c1b04..42d4136ed6ac 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2195,12 +2195,8 @@ void cpu_init_exception_handling(void)
/* GHCB needs to be setup to handle #VC. */
setup_ghcb();
- if (cpu_feature_enabled(X86_FEATURE_FRED)) {
- cpu_init_fred_exceptions();
- cpu_init_fred_rsps();
- } else {
+ if (!cpu_feature_enabled(X86_FEATURE_FRED))
load_current_idt();
- }
}
/*
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 728927e4ba51..36403b901eb2 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -39,6 +39,7 @@
#include <asm/coco.h>
#include <asm/cpu.h>
#include <asm/efi.h>
+#include <asm/fred.h>
#include <asm/gart.h>
#include <asm/hypervisor.h>
#include <asm/io_apic.h>
@@ -1040,7 +1041,15 @@ void __init setup_arch(char **cmdline_p)
init_mem_mapping();
- idt_setup_early_pf();
+ /*
+ * init_mem_mapping() uses early IDT to setup memory mappings, thus FRED
+ * can't be enabled earlier than that, unless FRED adds support to setup
+ * memory mappings.
+ */
+ if (cpu_feature_enabled(X86_FEATURE_FRED))
+ cpu_init_fred_exceptions();
+ else
+ idt_setup_early_pf();
/*
* Update mmu_cr4_features (and, indirectly, trampoline_cr4_features)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 0c35207320cb..0d83377f9dcd 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -64,6 +64,7 @@
#include <asm/acpi.h>
#include <asm/cacheinfo.h>
#include <asm/desc.h>
+#include <asm/fred.h>
#include <asm/nmi.h>
#include <asm/irq.h>
#include <asm/realmode.h>
@@ -248,6 +249,11 @@ static void notrace start_secondary(void *unused)
cpu_init_exception_handling();
+ if (cpu_feature_enabled(X86_FEATURE_FRED)) {
+ cpu_init_fred_exceptions();
+ cpu_init_fred_rsps();
+ }
+
/*
* Load the microcode before reaching the AP alive synchronization
* point below so it is not part of the full per CPU serialized
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 6afb41e6cbbb..81648bd07576 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1407,6 +1407,10 @@ void __init trap_init(void)
/* Init cpu_entry_area before IST entries are set up */
setup_cpu_entry_areas();
+ /* FRED RSPs pointing to memory from CPU entry areas */
+ if (cpu_feature_enabled(X86_FEATURE_FRED))
+ cpu_init_fred_rsps();
+
/* Init GHCB memory pages when running as an SEV-ES guest */
sev_es_init_vc_handling();
--
2.45.2On Tue, Jul 09 2024 at 08:40, Xin Li wrote:
I'm really unhappy about sprinkling all these FRED conditionals all over
the place:
> init_mem_mapping();
>
> - idt_setup_early_pf();
> + /*
> + * init_mem_mapping() uses early IDT to setup memory mappings, thus FRED
> + * can't be enabled earlier than that, unless FRED adds support to setup
> + * memory mappings.
> + */
> + if (cpu_feature_enabled(X86_FEATURE_FRED))
> + cpu_init_fred_exceptions();
> + else
> + idt_setup_early_pf();
> @@ -248,6 +249,11 @@ static void notrace start_secondary(void *unused)
>
> cpu_init_exception_handling();
>
> + if (cpu_feature_enabled(X86_FEATURE_FRED)) {
> + cpu_init_fred_exceptions();
> + cpu_init_fred_rsps();
> + }
> /* Init cpu_entry_area before IST entries are set up */
> setup_cpu_entry_areas();
>
> + /* FRED RSPs pointing to memory from CPU entry areas */
> + if (cpu_feature_enabled(X86_FEATURE_FRED))
> + cpu_init_fred_rsps();
> +
> /* Init GHCB memory pages when running as an SEV-ES guest */
> sev_es_init_vc_handling();
This really can be encapsulated and kept in places which need to know
about FRED already. See below. Can you please validate?
Thanks,
tglx
---
From: "Xin Li (Intel)" <xin@zytor.com>
Subject: x86/fred: Enable FRED right after init_mem_mapping()
Date: Tue, 09 Jul 2024 08:40:48 -0700
From: "Xin Li (Intel)" <xin@zytor.com>
On 64-bit init_mem_mapping() relies on the minimal page fault handler
provided by the early IDT mechanism. The real page fault handler is
installed right afterwards into the IDT.
This is problematic on CPUs which have X86_FEATURE_FRED set because the
real page fault handler retrieves the faulting address from the FRED
exception stack frame and not from CR2, but that does obviously not work
when FRED is not yet enabled in the CPU.
To prevent this enable FRED right after init_mem_mapping() without
interrupt stacks. Those are enabled later in trap_init() after the CPU
entry area is set up.
[ tglx: Encapsulate the FRED details ]
Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240709154048.3543361-4-xin@zytor.com
---
arch/x86/include/asm/processor.h | 3 ++-
arch/x86/kernel/cpu/common.c | 15 +++++++++++++--
arch/x86/kernel/setup.c | 7 ++++++-
arch/x86/kernel/smpboot.c | 2 +-
arch/x86/kernel/traps.c | 2 +-
5 files changed, 23 insertions(+), 6 deletions(-)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -582,7 +582,8 @@ extern void switch_gdt_and_percpu_base(i
extern void load_direct_gdt(int);
extern void load_fixmap_gdt(int);
extern void cpu_init(void);
-extern void cpu_init_exception_handling(void);
+extern void cpu_init_exception_handling(bool boot_cpu);
+extern void cpu_init_replace_early_idt(void);
extern void cr4_init(void);
extern void set_task_blockstep(struct task_struct *task, bool on);
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2176,7 +2176,7 @@ static inline void tss_setup_io_bitmap(s
* Setup everything needed to handle exceptions from the IDT, including the IST
* exceptions which use paranoid_entry().
*/
-void cpu_init_exception_handling(void)
+void cpu_init_exception_handling(bool boot_cpu)
{
struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
int cpu = raw_smp_processor_id();
@@ -2196,13 +2196,24 @@ void cpu_init_exception_handling(void)
setup_ghcb();
if (cpu_feature_enabled(X86_FEATURE_FRED)) {
- cpu_init_fred_exceptions();
+ /* The boot CPU has enabled FRED during early boot */
+ if (!boot_cpu)
+ cpu_init_fred_exceptions();
+
cpu_init_fred_rsps();
} else {
load_current_idt();
}
}
+void __init cpu_init_replace_early_idt(void)
+{
+ if (cpu_feature_enabled(X86_FEATURE_FRED))
+ cpu_init_fred_exceptions();
+ else
+ idt_setup_early_pf();
+}
+
/*
* cpu_init() initializes state that is per-CPU. Some data is already
* initialized (naturally) in the bootstrap process, such as the GDT. We
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1039,7 +1039,12 @@ void __init setup_arch(char **cmdline_p)
init_mem_mapping();
- idt_setup_early_pf();
+ /*
+ * init_mem_mapping() relies on the early IDT page fault handling.
+ * Now either enable FRED or install the real page fault handler
+ * for 64-bit in the IDT.
+ */
+ cpu_init_replace_early_idt();
/*
* Update mmu_cr4_features (and, indirectly, trampoline_cr4_features)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -246,7 +246,7 @@ static void notrace start_secondary(void
__flush_tlb_all();
}
- cpu_init_exception_handling();
+ cpu_init_exception_handling(false);
/*
* Load the microcode before reaching the AP alive synchronization
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1411,7 +1411,7 @@ void __init trap_init(void)
sev_es_init_vc_handling();
/* Initialize TSS before setting up traps so ISTs work */
- cpu_init_exception_handling();
+ cpu_init_exception_handling(true);
/* Setup traps as cpu_init() might #GP */
if (!cpu_feature_enabled(X86_FEATURE_FRED))
On 8/13/2024 5:45 AM, Thomas Gleixner wrote:
> On Tue, Jul 09 2024 at 08:40, Xin Li wrote:
>
> I'm really unhappy about sprinkling all these FRED conditionals all over
> the place:
Sigh, for the reason of a bad taste...
>> init_mem_mapping();
>>
>> - idt_setup_early_pf();
>> + /*
>> + * init_mem_mapping() uses early IDT to setup memory mappings, thus FRED
>> + * can't be enabled earlier than that, unless FRED adds support to setup
>> + * memory mappings.
>> + */
>> + if (cpu_feature_enabled(X86_FEATURE_FRED))
>> + cpu_init_fred_exceptions();
>> + else
>> + idt_setup_early_pf();
>
>> @@ -248,6 +249,11 @@ static void notrace start_secondary(void *unused)
>>
>> cpu_init_exception_handling();
>>
>> + if (cpu_feature_enabled(X86_FEATURE_FRED)) {
>> + cpu_init_fred_exceptions();
>> + cpu_init_fred_rsps();
>> + }
>
>> /* Init cpu_entry_area before IST entries are set up */
>> setup_cpu_entry_areas();
>>
>> + /* FRED RSPs pointing to memory from CPU entry areas */
>> + if (cpu_feature_enabled(X86_FEATURE_FRED))
>> + cpu_init_fred_rsps();
>> +
>> /* Init GHCB memory pages when running as an SEV-ES guest */
>> sev_es_init_vc_handling();
>
> This really can be encapsulated and kept in places which need to know
> about FRED already. See below. Can you please validate?
I reviewed your patch, and there is no reason it won't work; my tests
show no problem with it.
Thanks!
Xin
> ---
> From: "Xin Li (Intel)" <xin@zytor.com>
> Subject: x86/fred: Enable FRED right after init_mem_mapping()
> Date: Tue, 09 Jul 2024 08:40:48 -0700
>
> From: "Xin Li (Intel)" <xin@zytor.com>
>
> On 64-bit init_mem_mapping() relies on the minimal page fault handler
> provided by the early IDT mechanism. The real page fault handler is
> installed right afterwards into the IDT.
>
> This is problematic on CPUs which have X86_FEATURE_FRED set because the
> real page fault handler retrieves the faulting address from the FRED
> exception stack frame and not from CR2, but that does obviously not work
> when FRED is not yet enabled in the CPU.
>
> To prevent this enable FRED right after init_mem_mapping() without
> interrupt stacks. Those are enabled later in trap_init() after the CPU
> entry area is set up.
>
> [ tglx: Encapsulate the FRED details ]
>
> Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
> Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Link: https://lore.kernel.org/all/20240709154048.3543361-4-xin@zytor.com
> ---
> arch/x86/include/asm/processor.h | 3 ++-
> arch/x86/kernel/cpu/common.c | 15 +++++++++++++--
> arch/x86/kernel/setup.c | 7 ++++++-
> arch/x86/kernel/smpboot.c | 2 +-
> arch/x86/kernel/traps.c | 2 +-
> 5 files changed, 23 insertions(+), 6 deletions(-)
>
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -582,7 +582,8 @@ extern void switch_gdt_and_percpu_base(i
> extern void load_direct_gdt(int);
> extern void load_fixmap_gdt(int);
> extern void cpu_init(void);
> -extern void cpu_init_exception_handling(void);
> +extern void cpu_init_exception_handling(bool boot_cpu);
> +extern void cpu_init_replace_early_idt(void);
> extern void cr4_init(void);
>
> extern void set_task_blockstep(struct task_struct *task, bool on);
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -2176,7 +2176,7 @@ static inline void tss_setup_io_bitmap(s
> * Setup everything needed to handle exceptions from the IDT, including the IST
> * exceptions which use paranoid_entry().
> */
> -void cpu_init_exception_handling(void)
> +void cpu_init_exception_handling(bool boot_cpu)
> {
> struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
> int cpu = raw_smp_processor_id();
> @@ -2196,13 +2196,24 @@ void cpu_init_exception_handling(void)
> setup_ghcb();
>
> if (cpu_feature_enabled(X86_FEATURE_FRED)) {
> - cpu_init_fred_exceptions();
> + /* The boot CPU has enabled FRED during early boot */
> + if (!boot_cpu)
> + cpu_init_fred_exceptions();
> +
> cpu_init_fred_rsps();
> } else {
> load_current_idt();
> }
> }
>
> +void __init cpu_init_replace_early_idt(void)
> +{
> + if (cpu_feature_enabled(X86_FEATURE_FRED))
> + cpu_init_fred_exceptions();
> + else
> + idt_setup_early_pf();
> +}
> +
> /*
> * cpu_init() initializes state that is per-CPU. Some data is already
> * initialized (naturally) in the bootstrap process, such as the GDT. We
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -1039,7 +1039,12 @@ void __init setup_arch(char **cmdline_p)
>
> init_mem_mapping();
>
> - idt_setup_early_pf();
> + /*
> + * init_mem_mapping() relies on the early IDT page fault handling.
> + * Now either enable FRED or install the real page fault handler
> + * for 64-bit in the IDT.
> + */
> + cpu_init_replace_early_idt();
>
> /*
> * Update mmu_cr4_features (and, indirectly, trampoline_cr4_features)
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -246,7 +246,7 @@ static void notrace start_secondary(void
> __flush_tlb_all();
> }
>
> - cpu_init_exception_handling();
> + cpu_init_exception_handling(false);
>
> /*
> * Load the microcode before reaching the AP alive synchronization
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -1411,7 +1411,7 @@ void __init trap_init(void)
> sev_es_init_vc_handling();
>
> /* Initialize TSS before setting up traps so ISTs work */
> - cpu_init_exception_handling();
> + cpu_init_exception_handling(true);
>
> /* Setup traps as cpu_init() might #GP */
> if (!cpu_feature_enabled(X86_FEATURE_FRED))
>
The following commit has been merged into the x86/fred branch of tip:
Commit-ID: a97756cbec448032f84b5bbfe4e101478d1e01e0
Gitweb: https://git.kernel.org/tip/a97756cbec448032f84b5bbfe4e101478d1e01e0
Author: Xin Li (Intel) <xin@zytor.com>
AuthorDate: Tue, 09 Jul 2024 08:40:48 -07:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 13 Aug 2024 21:59:21 +02:00
x86/fred: Enable FRED right after init_mem_mapping()
On 64-bit init_mem_mapping() relies on the minimal page fault handler
provided by the early IDT mechanism. The real page fault handler is
installed right afterwards into the IDT.
This is problematic on CPUs which have X86_FEATURE_FRED set because the
real page fault handler retrieves the faulting address from the FRED
exception stack frame and not from CR2, but that does obviously not work
when FRED is not yet enabled in the CPU.
To prevent this enable FRED right after init_mem_mapping() without
interrupt stacks. Those are enabled later in trap_init() after the CPU
entry area is set up.
[ tglx: Encapsulate the FRED details ]
Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
Reported-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240709154048.3543361-4-xin@zytor.com
---
arch/x86/include/asm/processor.h | 3 ++-
arch/x86/kernel/cpu/common.c | 15 +++++++++++++--
arch/x86/kernel/setup.c | 7 ++++++-
arch/x86/kernel/smpboot.c | 2 +-
arch/x86/kernel/traps.c | 2 +-
5 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index a75a07f..399f7d1 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -582,7 +582,8 @@ extern void switch_gdt_and_percpu_base(int);
extern void load_direct_gdt(int);
extern void load_fixmap_gdt(int);
extern void cpu_init(void);
-extern void cpu_init_exception_handling(void);
+extern void cpu_init_exception_handling(bool boot_cpu);
+extern void cpu_init_replace_early_idt(void);
extern void cr4_init(void);
extern void set_task_blockstep(struct task_struct *task, bool on);
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 6de12b3..a4735d9 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -2176,7 +2176,7 @@ static inline void tss_setup_io_bitmap(struct tss_struct *tss)
* Setup everything needed to handle exceptions from the IDT, including the IST
* exceptions which use paranoid_entry().
*/
-void cpu_init_exception_handling(void)
+void cpu_init_exception_handling(bool boot_cpu)
{
struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
int cpu = raw_smp_processor_id();
@@ -2196,13 +2196,24 @@ void cpu_init_exception_handling(void)
setup_ghcb();
if (cpu_feature_enabled(X86_FEATURE_FRED)) {
- cpu_init_fred_exceptions();
+ /* The boot CPU has enabled FRED during early boot */
+ if (!boot_cpu)
+ cpu_init_fred_exceptions();
+
cpu_init_fred_rsps();
} else {
load_current_idt();
}
}
+void __init cpu_init_replace_early_idt(void)
+{
+ if (cpu_feature_enabled(X86_FEATURE_FRED))
+ cpu_init_fred_exceptions();
+ else
+ idt_setup_early_pf();
+}
+
/*
* cpu_init() initializes state that is per-CPU. Some data is already
* initialized (naturally) in the bootstrap process, such as the GDT. We
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 6129dc2..f1fea50 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1039,7 +1039,12 @@ void __init setup_arch(char **cmdline_p)
init_mem_mapping();
- idt_setup_early_pf();
+ /*
+ * init_mem_mapping() relies on the early IDT page fault handling.
+ * Now either enable FRED or install the real page fault handler
+ * for 64-bit in the IDT.
+ */
+ cpu_init_replace_early_idt();
/*
* Update mmu_cr4_features (and, indirectly, trampoline_cr4_features)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 0c35207..dc4fff8 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -246,7 +246,7 @@ static void notrace start_secondary(void *unused)
__flush_tlb_all();
}
- cpu_init_exception_handling();
+ cpu_init_exception_handling(false);
/*
* Load the microcode before reaching the AP alive synchronization
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 6afb41e..197d588 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -1411,7 +1411,7 @@ void __init trap_init(void)
sev_es_init_vc_handling();
/* Initialize TSS before setting up traps so ISTs work */
- cpu_init_exception_handling();
+ cpu_init_exception_handling(true);
/* Setup traps as cpu_init() might #GP */
if (!cpu_feature_enabled(X86_FEATURE_FRED))© 2016 - 2025 Red Hat, Inc.