Re: [RFC PATCH v3 17/36] pflash_cfi01/tdx: Introduce ram_mode of pflash for TDVF

[Xiaoyao Li]

On 3/22/2022 5:27 PM, Daniel P. Berrangé wrote:
...
> IMHO the AmdSev build for OVMF gets this right by entirely disabling
> the split OVMF_CODE.fd vs OVMF_VARS.fd, and just having a single
> OVMF.fd file that is exposed read-only to the guest.
>
> This is further represented in $QEMU.git/docs/interop/firmware.json
> by marking the firmware as 'stateless', which apps like libvirt will
> use to figure out what QEMU command line to pick.

Hi Daniel,

I don't play with AMD SEV and I'm not sure if AMD SEV requires only 
single OVMF.fd. But IIUC, from edk2

commit 437eb3f7a8db ("OvmfPkg/QemuFlashFvbServicesRuntimeDxe: Bypass 
flash detection with SEV-ES")

, AMD SEV(-ES) does support NVRAM via proactive VMGEXIT MMIO 
QemuFlashWrite(). If so, AMD SEV seems to be able to support split OVMF, 
right?

> IOW, if you don't want OVMF_VARS.fd to be written to, then follow
> what AmdSev has done, and get rid of the split files.
>
>
> With regards,
> Daniel