Messages in this thread | | | Date | Fri, 13 Nov 2015 16:19:13 +0000 | From | Matt Fleming <> | Subject | Re: [PATCH 4/6] x86/efi: Hoist page table switching code into efi_call_virt() |
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On Fri, 13 Nov, at 08:59:43AM, Borislav Petkov wrote: > On Thu, Nov 12, 2015 at 08:01:08PM +0000, Matt Fleming wrote: > > > That PUSHF implicitly pushes on the stack pointed by %rsp. But(!) we > > > have switched the pagetable (i.e., %cr3 has efi_scratch.efi_pgt) and > > > we're pushing to the VA where the stack *was* but is not anymore. > > > > All the kernel mappings will still exist in the page table we switch > > to, so pushing to the stack should be fine. > > > > The mappings have to exist so that the firmware can dereference > > pointer arguments, e.g. when writing variable data to a kernel buffer. > > > > Or have I misunderstood your point? > > > > > Or maybe it is because you're copying all the PUDs. It is still not 100% > > > clean, IMHO. > ^^^^^^^^^^^^^^^^^ > > I think we're on the same page - you're copying the PUDs in > efi_sync_low_kernel_mappings() so the stack should be there.
Correct.
> > > Can you do the prolog/epilog calls inside the IRQs-off section? > > > > Not really because in the efi_enabled(EFI_OLD_MEMMAP) case we perform > > kmalloc(), see commit 23a0d4e8fa6d ("efi: Disable interrupts around > > EFI calls, not in the epilog/prolog calls"). > > n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE); > save_pgd = kmalloc(n_pgds * sizeof(pgd_t), GFP_KERNEL); > > This? > > That n_pgds thing is of static size so you can pre-alloc it maybe even > once during boot and reuse it all the time when EFI_OLD_MEMMAP is > enabled.
Well, this code is only executed once during boot anyway, for phys_efi_set_virtual_address_map().
FYI, I'm still planning on ripping out all the EFI_OLD_MEMMAP code, as it's getting particularly crufty.
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