Messages in this thread | | | Date | Thu, 28 Apr 2016 14:57:11 +0200 | From | Borislav Petkov <> | Subject | Re: [BUG] x86/efi: MMRs no longer properly mapped after switch to isolated page table |
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On Wed, Apr 27, 2016 at 08:41:28PM -0500, Alex Thorlton wrote: > In this particular instance, it's not using the EFI page table - it's > showing that the register isn't mapped into the main kernel page table, > via the bad paging request. The issue isn't that there's something > wrong with the EFI page table, but that something appears to be missing > from the kernel table.
So my question stands: you said 67a9108ed4313 is causing this and this commit creates an EFI-specific page table and that shouldn't have anything to do with how the MMR stuff is mapped, should it?
> Well, quite a while back, these MMRs got mapped in using > init_extra_mapping_uc in map_low_mmrs. Back then, yes, they were mapped > straight into the kernel page table. > > After d2f7cbe7b26a74 ("x86/efi: Runtime services virtual mapping") was > introduced (I'm sure you remember the BIOS issue we had a while back) we > had to fall back to using EFI_OLD_MEMMAP, so for a while we relied on > efi_ioremap.
Hmm, but you see my confusion, right? Why is init_extra_mapping_uc() influenced by the EFI changes? It uses __init_extra_mapping() and it maps into init_mm's pgd.
> Eventually we got a BIOS fix that allowed us to start using the new > memmap scheme, at which point we removed the init_extra_mapping_uc()s, > since the efi_map_region code appeared to be doing what we needed.
Why would you even do that? Why are you even mapping MMRs using EFI facilities?
I'm more confused today.
So what I see from here is this:
* MMRs and EFI shouldn't have anything in common. Imagine there were an UV box without EFI (you probably are going to say there's no such thing but imagine anyway): how are you going to map the MMR space then?
* I think you should restore the old case where you mapped the MMRs using init_extra_mapping_uc().
And I think
d394f2d9d8e1 ("x86/platform/UV: Remove EFI memmap quirk for UV2+")
was wrong in doing
+ if (is_uv1_hub()) + map_low_mmrs();
for the simple fact that MMRs mapping and EFI shouldn't depend on one another.
So the proper fix would be to remove the if- check.
Or am I missing something here and MMRs need EFI?
(However, UV1 apparently works fine without it).
Right?
-- Regards/Gruss, Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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