Re: [GIT PULL] x86/uapi for 3.8

From: Jan Beulich
Date: Mon Dec 17 2012 - 11:00:53 EST

>>> On 17.12.12 at 16:44, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Dec 17, 2012 at 1:04 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> How about this being caused by using the same lower level
>> page table entries that swapper_pg_dir uses, namely including
>> the _PAGE_GLOBAL bits? efi_call_virt_{pre,epi}log() only write
>> CR3 (see 185034e72d591f9465e5e18f937ed642e7ea0070), but
>> would need to also flip CR4.PGE afaict.
> Now *this* is the kind of issue that I could easily see causing major
> corruption, but be subtle enough to not happen reliably. Coming back
> from the EFI calls (or going into them) with stale TLB contents due to
> global pages could explain things.
> Good thinking. That efi call code should use flush_tlb_kernel() (or
> __flush_tlb_global() if it wants to avoid any paravirtualization
> stuff) if it has global pages in different places from the normal
> kernel map. Does it really have that?

I don't see it having such. But I also don't think flush_tlb_kernel()
is the right mechanism here. I'd rather suggest clearing CR4.PGE in
the "prelog", an restore it in the epilog. Para-virtual environments
shouldn't be directly interfacing with EFI runtime code anyway.


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