* Gerd Hoffmann <kraxel@xxxxxxxxxx> wrote:
> In case efi_mm is active go use the userspace instruction decoder which
> supports fetching instructions from active_mm. This is needed to make
> instruction emulation work for EFI runtime code, so it can use cpuid
> and rdmsr.
>
> EFI runtime code uses the cpuid instruction to gather information about
> the environment it is running in, such as SEV being enabled or not, and
> choose (if needed) the SEV code path for ioport access.
>
> EFI runtime code uses the rdmsr instruction to get the location of the
> CAA page (see SVSM spec, section 4.2 - "Post Boot").
>
> The big picture behind this is that the kernel needs to be able to
> properly handle #VC exceptions that come from EFI runtime services.
> Since EFI runtime services have a special page table mapping for the EFI
> virtual address space, the efi_mm context must be used when decoding
> instructions during #VC handling.
>
> Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
> ---
> arch/x86/coco/sev/vc-handle.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/coco/sev/vc-handle.c b/arch/x86/coco/sev/vc-handle.c
> index 0989d98da130..e498a8965939 100644
> --- a/arch/x86/coco/sev/vc-handle.c
> +++ b/arch/x86/coco/sev/vc-handle.c
> @@ -17,6 +17,7 @@
> #include <linux/mm.h>
> #include <linux/io.h>
> #include <linux/psp-sev.h>
> +#include <linux/efi.h>
> #include <uapi/linux/sev-guest.h>
>
> #include <asm/init.h>
> @@ -178,9 +179,14 @@ static enum es_result __vc_decode_kern_insn(struct es_em_ctxt *ctxt)
> return ES_OK;
> }
>
> +/*
> + * User instruction decoding is also required for the EFI runtime. Even though
> + * EFI runtime is running in kernel mode, it uses special EFI virtual address
s/Even though EFI runtime
/Even though the EFI runtime
> + * mappings that require the use of efi_mm to properly address and decode.
> + */
> static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
> {
> - if (user_mode(ctxt->regs))
> + if (user_mode(ctxt->regs) || current->active_mm == &efi_mm)
Instead of open-coding that condition, we have mm_is_efi() for that.
Thanks,
Ingo
