Re: [PATCH v4] EFI: always map EfiRuntimeServices{Code,Data}

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.01.2022 11:45, Julien Grall wrote:
> On 12/01/2022 08:45, Jan Beulich wrote:
>> From: Sergey Temerkhanov <s.temerkhanov@xxxxxxxxx>
>>
>> This helps overcome problems observed with some UEFI implementations
> 
> Would it be possible to provide some details about the platform? This is 
> helpful to track why a workaround is present.

I cannot provide any details. I took over the patch after pinging
Sergey more than once, without any reaction. It was him to actually
run into the problem in the wild.

>> which don't set the Attributes field in memery descriptors properly.
> 
> typo: s/memery/memory/
> 
>>
>> Signed-off-by: Sergey Temerkhanov <s.temerkhanov@xxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> v4: Drop EFI_MEMORY_CACHEABILITY_MASK. Fold with pre-existing if() (into
>>      switch()). Style.
>> ---
>> I guess "map_bs" would also want honoring in efi_exit_boot(), but that's
>> yet another patch then I suppose.
> 
> IIUC, we would need to invalidate the mapping when map_bs was used. Is 
> it correct? If so, then I agree this sounds separate to the issue you 
> are describing here.

No, the other way around: We'd also need to put in a valid virtual
address there for EfiBootServices{Code,Data}. I expect this wasn't
done when map_bs was introduced because iirc at that time the code
fragment in efi_exit_boot() was entirely dead, present merely for
documentation purposes.

>> --- a/xen/common/efi/boot.c
>> +++ b/xen/common/efi/boot.c
>> @@ -1094,7 +1094,13 @@ static void __init efi_exit_boot(EFI_HAN
>>       {
>>           EFI_MEMORY_DESCRIPTOR *desc = efi_memmap + i;
>>   
>> -        if ( desc->Attribute & EFI_MEMORY_RUNTIME )
>> +        /*
>> +         * Runtime services regions are always mapped here.
>> +         * Attributes may be adjusted in efi_init_memory().
>> +         */
>> +        if ( (desc->Attribute & EFI_MEMORY_RUNTIME) ||
>> +             desc->Type == EfiRuntimeServicesCode ||
>> +             desc->Type == EfiRuntimeServicesData )
> 
> My knowledge with the stub is limited. Would you be able to explain why 
> we need to map the runtime services even with !efi_enabled(EFI_RS)?

In principle we wouldn't need to, but the final setting of this bit
isn't known yet at this point - it'll be known only after parsing
the command line (see parse_efi_param()).

Jan