Re: [PATCH] x86, efi: 1:1 pagetable mapping for virtual EFIcalls

[Jan Beulich]

>>> On 06.09.12 at 17:47, Matt Fleming <matt.fleming@xxxxxxxxx> wrote:
> On Thu, 2012-09-06 at 15:34 +0100, Jan Beulich wrote:
>> >>> On 06.09.12 at 15:15, Matt Fleming <matt@xxxxxxxxxxxxxxxxx> wrote:
>> > +
>> > +		pgd += i;
>> > +		save[i] = *pgd;
>> > +		set_pgd(pgd, efi_one_to_one_pgd[i]);
>> > +	}
>> 
>> Did you, as an alternative, consider switching to a different
>> CR3 instead of copying back and forth?
> 
> I did consider it, but I couldn't convince myself whether or not the EFI
> pagetable would need to be manually kept in sync with any other
> pagetables. But now I look at the code a bit harder, it seems that
> should be taken care of automatically. In fact, the tboot code seems to
> do something similar. I'll try that approach.

Actually, I think the copying approach is even broken - what if
multiple threads currently on the same address space want to
invoke a runtime call simultaneously? The first one to get here
would save the right values, but the second one wouldn't.

Jan

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