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

["Philippe Mathieu-Daudé" <philippe.mathieu.daude@gmail.com>]

Hi,

On 17/3/22 14:58, Xiaoyao Li wrote:
> TDX VM needs to boot with Trust Domain Virtual Firmware (TDVF). Unlike
> that OVMF is mapped as rom device, TDVF needs to be mapped as private
> memory. This is because TDX architecture doesn't provide read-only
> capability for VMM, and it doesn't support instruction emulation due
> to guest memory and registers are not accessible for VMM.
> 
> On the other hand, OVMF can work as TDVF, which is usually configured
> as pflash device in QEMU. To keep the same usage (QEMU parameter),
> introduce ram_mode to pflash for TDVF. When it's creating a TDX VM,
> ram_mode will be enabled automatically that map the firmware as RAM.
> 
> Note, this implies two things:
>   1. TDVF (OVMF) is not read-only (write-protected).
> 
>   2. It doesn't support non-volatile UEFI variables as what pflash
>      supports that the change to non-volatile UEFI variables won't get
>      synced back to backend vars.fd file.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>   hw/block/pflash_cfi01.c | 25 ++++++++++++++++++-------
>   hw/i386/pc_sysfw.c      | 14 +++++++++++---
>   2 files changed, 29 insertions(+), 10 deletions(-)

If you don't need a pflash device, don't use it: simply map your nvram
region as ram in your machine. No need to clutter the pflash model like
that.

NAcked-by: Philippe Mathieu-Daudé <f4bug@amsat.org>