From: Julien Grall <jgrall@amazon.com>

When using EFI, the VGA information is fetched using the EFI
boot services. However, Xen will have exited the boot services.
Therefore, we need to find a different way to pass the information
to dom0.

For PV dom0, they are part of the start_info. But this is not
something that exists on Arm. So the best way would to be to
use a hypercall.

For now the structure layout is based on dom0_vga_console_info
for convenience. I am open on another proposal.

Signed-off-by: Julien Grall <jgrall@amazon.com>

----

TODO:
    - Check the structure size has not changed (I would like to
      avoid bumping the platform interface).
---
 xen/arch/arm/platform_hypercall.c | 15 +++++++++++++++
 xen/include/public/platform.h     |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/xen/arch/arm/platform_hypercall.c b/xen/arch/arm/platform_hypercall.c
index 8efac7ee602a..78ad328e2ab8 100644
--- a/xen/arch/arm/platform_hypercall.c
+++ b/xen/arch/arm/platform_hypercall.c
@@ -10,6 +10,7 @@
 #include <xen/sched.h>
 #include <xen/guest_access.h>
 #include <xen/spinlock.h>
+#include <xen/vga.h>
 #include <public/platform.h>
 #include <xsm/xsm.h>
 #include <asm/current.h>
@@ -58,6 +59,20 @@ long do_platform_op(XEN_GUEST_HANDLE_PARAM(xen_platform_op_t) u_xenpf_op)
             ret = -EINVAL;
         break;
 
+    case XENPF_firmware_info:
+        switch ( op->u.firmware_info.type )
+        {
+        case XEN_FW_VGA_INFO:
+            BUILD_BUG_ON(sizeof(op->u.firmware_info.u.vga) !=
+                         sizeof(vga_console_info));
+            memcpy(&op->u.firmware_info.u.vga, &vga_console_info,
+                   sizeof(vga_console_info));
+            if ( __copy_to_guest(u_xenpf_op, op, 1) )
+                ret = -EFAULT;
+            break;
+        }
+        break;
+
     default:
         ret = -ENOSYS;
         break;
diff --git a/xen/include/public/platform.h b/xen/include/public/platform.h
index a4c0eb62249a..4de42ce6cbc5 100644
--- a/xen/include/public/platform.h
+++ b/xen/include/public/platform.h
@@ -244,6 +244,7 @@ DEFINE_XEN_GUEST_HANDLE(xenpf_efi_runtime_call_t);
 #define  XEN_FW_EFI_PCI_ROM        5
 #define  XEN_FW_EFI_APPLE_PROPERTIES 6
 #define XEN_FW_KBD_SHIFT_FLAGS    5
+#define XEN_FW_VGA_INFO           6
 struct xenpf_firmware_info {
     /* IN variables. */
     uint32_t type;
@@ -311,6 +312,7 @@ struct xenpf_firmware_info {
 
         /* Int16, Fn02: Get keyboard shift flags. */
         uint8_t kbd_shift_flags; /* XEN_FW_KBD_SHIFT_FLAGS */
+        struct dom0_vga_console_info vga;
     } u;
 };
 typedef struct xenpf_firmware_info xenpf_firmware_info_t;
-- 
2.32.0

On 06.02.2022 20:28, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> When using EFI, the VGA information is fetched using the EFI
> boot services. However, Xen will have exited the boot services.
> Therefore, we need to find a different way to pass the information
> to dom0.
> 
> For PV dom0, they are part of the start_info. But this is not
> something that exists on Arm. So the best way would to be to
> use a hypercall.
> 
> For now the structure layout is based on dom0_vga_console_info
> for convenience. I am open on another proposal.
> 
> Signed-off-by: Julien Grall <jgrall@amazon.com>

Cc-ing Roger as this may want using for PVH Dom0 also on x86; my
first attempt to propagate this information was rejected.

> --- a/xen/include/public/platform.h
> +++ b/xen/include/public/platform.h
> @@ -244,6 +244,7 @@ DEFINE_XEN_GUEST_HANDLE(xenpf_efi_runtime_call_t);
>  #define  XEN_FW_EFI_PCI_ROM        5
>  #define  XEN_FW_EFI_APPLE_PROPERTIES 6
>  #define XEN_FW_KBD_SHIFT_FLAGS    5
> +#define XEN_FW_VGA_INFO           6

Perhaps s/VGA/VIDEO/, despite ...

>  struct xenpf_firmware_info {
>      /* IN variables. */
>      uint32_t type;
> @@ -311,6 +312,7 @@ struct xenpf_firmware_info {
>  
>          /* Int16, Fn02: Get keyboard shift flags. */
>          uint8_t kbd_shift_flags; /* XEN_FW_KBD_SHIFT_FLAGS */
> +        struct dom0_vga_console_info vga;

... the structure name including "vga" (but if the #define is adjusted,
the field name would want to become "video" as well).

Jan