On Wed, 25 Jan, at 09:31:53PM, Jiri Kosina wrote:
>
> [ CCing mailinglists that got eaten by my newly configured mail setup,
> sorry for that ]
>
> On Wed, 25 Jan 2017, Jiri Kosina wrote:
>
> > From: Jiri Kosina <[email protected]>
> >
> > Commit 129766708 ("x86/efi: Only map RAM into EFI page tables if in
> > mixed-mode") stopped creating 1:1 mapping for all RAM in case of running
> > in native 64bit mode.
> >
> > It turns out though that there are 64bit EFI implementations in the wild
> > (this particular problem has been reported on Lenovo Yoga 710-11IKB) which
> > still make use of first physical page for their own private use (which is
> > what legacy BIOS used to do, but EFI specification doesn't grant any such
> > right to EFI BIOS ... oh well).
> >
> > In case there is no mapping for this particular frame in EFI pagetables,
> > as soon as firmware tries to make use of it, triple fault occurs and the
> > system reboots (in case of Yoga 710-11IKB this is very early during boot).
> >
The thing missing from this paragraph is that the EFI memmap entry
type for this page is EFI_CONVENTIONAL_MEMORY on these Lenovo Yoga's,
i.e. the firmware is telling the kernel that the first page is "free
memory" but will write to it anyway.
> > Fix that by always mapping the first page of physical memory into EFI
> > pagetables.
> >
> > Note: just reverting 129766708 is not enough on v4.9-rc1+ to fix the
> > regression on affected hardware, as commit ab72a27da ("x86/efi:
> > Consolidate region mapping logic") later made the first physical frame not
> > to be mapped anyway.
> >
> > Fixes: 129766708 ("x86/efi: Only map RAM into EFI page tables if in
> > mixed-mode")
> > Cc: [email protected] # v4.8+
> > Cc: Waiman Long <[email protected]>
> > Cc: Borislav Petkov <[email protected]>
> > Cc: Laura Abbott <[email protected]>
> > Cc: Vojtech Pavlik <[email protected]>
> > Reported-by: Hanka Pavlikova <[email protected]>
> > Signed-off-by: Jiri Kosina <[email protected]>
> > ---
> >
> > Thanks a lot to Matt for excellent hint how to debug EFI failures
> >
> > arch/x86/platform/efi/efi_64.c | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> > index 319148b..02ae2ab 100644
> > --- a/arch/x86/platform/efi/efi_64.c
> > +++ b/arch/x86/platform/efi/efi_64.c
> > @@ -269,6 +269,17 @@ int __init efi_setup_page_tables(unsigned long
> > pa_memmap, unsigned num_pages)
> > efi_scratch.use_pgd = true;
> >
> > /*
> > + * Certain firmware versions are way too sentimental and still believe
> > + * they are exclusive and unquestionable owners of first physical page.
> > + * Create 1:1 mapping for this page to avoid triple faults during early
> > + * boot with such firmware.
> > + */
> > + if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, _PAGE_RW)) {
> > + pr_err("Failed to create 1:1 mapping of first page\n");
> > + return 1;
> > + }
> > +
> > + /*
> > * When making calls to the firmware everything needs to be 1:1
> > * mapped and addressable with 32-bit pointers. Map the kernel
> > * text and allocate a new stack because we can't rely on the
Could you update the comment above to include two additional points:
1) We've seen machines that mark the first page as
EFI_CONVENTIONAL_MEMORY but the firmware will write to it
during SetVirtualAddressMap() nevertheless.
2) trim_bios_range() takes care of actually reserving the first page
and making it unavailable to the memory allocators.
