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

[Brijesh Singh]

On 5/4/21 2:55 PM, Brijesh Singh via groups.io 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.

Apologies, I missed the fact that you said document the mapping between
the PVALIDATE return value and EFI_STATUS. So a caller is responsible to
look at the EFI document to know what the error code means. The
unsupported here does not mean that PVALIDATE is not support on
platform. I am good with it. I will go ahead with it.

-Brijesh



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