Re: [tip:efi/core] x86/mm/pat: Use _PAGE_GLOBAL bit for EFI page table mappings

From: Borislav Petkov
Date: Wed Feb 24 2016 - 11:20:15 EST

On Wed, Feb 24, 2016 at 02:10:46PM +0000, Matt Fleming wrote:
> > Normally, the only pages with are _PAGE_GLOBAL are those that are in
> > the normal kernel mappings (swapper_pg_dir and normal mm_struct pgds).
> > By allowing _PAGE_GLOBAL to be set in EFI mappings, you're breaking
> > that convention, which forces you to use extra-expensive
> > __flush_tlb_all calls in efi_call_virt.

Hold on, do you mean the __flush_tlb_all() in the CONFIG_EFI_MIXED code?

That's mixed mode. I think you mean the FLUSH_TLB_ALL in efi_call.
That's EFI on 64-bit but that is mandated by the spec, AFAIR.

So the EFI runtime crap should not change once it is mapped. And those
should be global. It is only natural.

> Nope. The "if (cpa->pgd)" guard ensures that we only call that
> function for the EFI mapping code - no one else sets ->pgd.

But it could - there's no guarantee. kernel_map_pages_in_pgd() is an
exported facility.


ECO tip #101: Trim your mails when you reply.