Re: [PATCH v2] x86/efi: always map first physical page into EFI pagetables

[Matt Fleming <matt@codeblueprint.co.uk>]

On Fri, 27 Jan, at 04:39:59PM, Jiri Kosina wrote:
> From: Jiri Kosina <jkosina@suse.cz>
> 
> 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 even 
> though they explicitly mark it EFI_CONVENTIONAL_MEMORY in the memory map.
> 
> 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. We're on a safe side, as trim_bios_range() will reserve the 
> first page and isolate it away from memory allocators anyway.
> 
> 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@kernel.org # v4.8+
> Cc: Waiman Long <waiman.long@hpe.com>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Laura Abbott <labbott@redhat.com>
> Cc: Vojtech Pavlik <vojtech@ucw.cz>
> Reported-by: Hanka Pavlikova <hanka@ucw.cz>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
> ---
 
Thanks Jiri. Queued for v4.10-rc6.