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



Hi Jan,

On 27/01/2022 12:25, Jan Beulich wrote:
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.

This is a quite unfortunate.


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()).

Oh. I thought efi_exit_boot() was called *after* efi_init_memory(). Your answer about 'map_bs' also make more sense.

Thanks for the explanation!

Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>

Cheers,

--
Julien Grall



 


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