[edk2-devel] [PATCH RFC v2 05/28] MdePkg: Add AsmPvalidate() support

[Laszlo Ersek]

On 05/04/21 21:55, Brijesh Singh wrote:
> 
> On 5/4/21 2:07 PM, Brijesh Singh via groups.io wrote:
>>> Return EFI_UNSUPPORTED (0x8000_0003), or even EFI_NO_MAPPING
>>> (0x8000_0017), for value 6 (FAIL_SIZEMISMATCH).
>> I am not sure if we really want to do this. You will see later in the
>> patches that in some cases the PVALIDATE will return a failure and we
>> will need to know the failure code to determine the next steps.
>> Especially this particular error code is used later. This error happens
>> when the page size of the backing pages does not match with the
>> pvalidated size. In those cases we need to retry the PVALIDATE with
>> lower page size so that a validation succeed. One such a example is:
>>
>> - Guest ask hypervisor to add the page as 2M in RMP table.
>>
>> - Hypervisor added the page as 512 4K pages - because it was not able to
>> find a large backing pages.
>>
>> - Guest attempts to pvalidate the page as a 2M. The pvalidate will
>> return a failure saying its a size mismatch between the requested
>> pvalidated and RMP table. The recommendation is that guest should try
>> with a smaller page size.
>>
>> I would prefer to pass the pvalidate error as-is to caller so that it
>> can make the correct decision.
>>
> I am perfectly fine if the function return UINTN and then use #define
> instead of the enum to define the PVALIDATE return code. So that caller
> can check the error code. Let me know your thought on #define instead of
> the enum.

(1) If the funcion returns UINTN rather than an enum type, that resolves
my request, technically speaking. I think it's inferior to the
EFI_STATUS mapping that I proposed, but it certainly resolves my request!

(2) How you provide the symbolic names for the values 0, 1, 6, does not
matter. If you use #define's (= macros), that's fine. If you use an enum
type, with enum constants, that's also fine. This aspect is orthogonal
to my request.

Thanks!
Laszlo



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