Re: [edk2-devel] [PATCH v8 26/46] OvmfPkg/VmgExitLib: Add support for DR7 Read/Write NAE events

["Laszlo Ersek" <lersek@redhat.com>]

On 05/19/20 23:50, Lendacky, Thomas wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
> 
> Under SEV-ES, a DR7 read or write intercept generates a #VC exception.
> The #VC handler must provide special support to the guest for this. On
> a DR7 write, the #VC handler must cache the value and issue a VMGEXIT
> to notify the hypervisor of the write. However, the #VC handler must
> not actually set the value of the DR7 register. On a DR7 read, the #VC
> handler must return the cached value of the DR7 register to the guest.
> VMGEXIT is not invoked for a DR7 register read.
> 
> To avoid exception recursion, a #VC exception will not try to read and
> push the actual debug registers into the EFI_SYSTEM_CONTEXT_X64 struct
> and instead push zeroes. The #VC exception handler does not make use of
> the debug registers from saved context.
> 
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  .../Library/VmgExitLib/X64/VmgExitVcHandler.c | 105 ++++++++++++++++++
>  .../X64/ExceptionHandlerAsm.nasm              |  17 +++
>  .../X64/Xcode5ExceptionHandlerAsm.nasm        |  17 +++
>  3 files changed, 139 insertions(+)

My brain is mush (the NPF/MMIO patch wasn't easy), so I'll pick up the
review at this patch next week.

Thanks!
Laszlo