[ 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 <jkosina@xxxxxxx>
>
> 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).
>
> 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: stable@xxxxxxxxxx # v4.8+
> Cc: Waiman Long <waiman.long@xxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Laura Abbott <labbott@xxxxxxxxxx>
> Cc: Vojtech Pavlik <vojtech@xxxxxx>
> Reported-by: Hanka Pavlikova <hanka@xxxxxx>
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
> ---
>
> 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
> --
> Jiri Kosina
> SUSE Labs
>
>
--
Jiri Kosina
SUSE Labs
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