[GIT PULL] EFI urgent fix

[GIT PULL] EFI urgent fix

[Matt Fleming]

Folks, please pull the below fix from Jiri which fixes a triple fault
affecting the Lenovo Yogas since v4.8.

The following changes since commit 7a308bb3016f57e5be11a677d15b821536419d36:

  Linux 4.10-rc5 (2017-01-22 12:54:15 -0800)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git tags/efi-urgent

for you to fetch changes up to 090abfc9dc7faf3f84799f956158c8c3af149a81:

  x86/efi: Always map first physical page into EFI pagetables (2017-01-27 20:20:01 +0000)

----------------------------------------------------------------
 * Fix triple fault on boot affecting Lenovo Yoga. The firmware on
   these machines will write to the zero page even though it's marked
   EFI_CONVENTIONAL_MEMORY, so we must ensure it's mapped in the EFI
   page tables - Jiri Kosina

----------------------------------------------------------------
Jiri Kosina (1):
      x86/efi: Always map first physical page into EFI pagetables

 arch/x86/platform/efi/efi_64.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

[GIT PULL] EFI urgent fix

[Matt Fleming]

Folks, please pull the below fix from Jiri which fixes a triple fault
affecting the Lenovo Yogas since v4.8.

The following changes since commit 7a308bb3016f57e5be11a677d15b821536419d36:

  Linux 4.10-rc5 (2017-01-22 12:54:15 -0800)

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/efi/efi.git tags/efi-urgent

for you to fetch changes up to 090abfc9dc7faf3f84799f956158c8c3af149a81:

  x86/efi: Always map first physical page into EFI pagetables (2017-01-27 20:20:01 +0000)

----------------------------------------------------------------
 * Fix triple fault on boot affecting Lenovo Yoga. The firmware on
   these machines will write to the zero page even though it's marked
   EFI_CONVENTIONAL_MEMORY, so we must ensure it's mapped in the EFI
   page tables - Jiri Kosina

----------------------------------------------------------------
Jiri Kosina (1):
      x86/efi: Always map first physical page into EFI pagetables

 arch/x86/platform/efi/efi_64.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

[PATCH] x86/efi: Always map first physical page into EFI pagetables

[Matt Fleming]

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.

Reported-by: Hanka Pavlikova <hanka@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Fixes: 129766708 ("x86/efi: Only map RAM into EFI page tables if in mixed-mode")
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
---
 arch/x86/platform/efi/efi_64.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 319148bd4b05..79c21cac1133 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -269,6 +269,22 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 	efi_scratch.use_pgd = true;
 
 	/*
+	 * Certain firmware versions are way too sentimential and still believe
+	 * they are exclusive and unquestionable owners of first physical page
+	 * even though they explicitly mark it as EFI_CONVENTIONAL_MEMORY
+	 * (but then write-access it later during SetVirtualAddressMap()).
+	 *
+	 * Create 1:1 mapping for this page to avoid triple faults during early
+	 * boot with such firmware. We're on a safe side, as trim_bios_range()
+	 * will reserve the first page and isolate it away from memory
+	 * allocators anyway.
+	 */
+	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
-- 
2.10.0

[PATCH] x86/efi: Always map first physical page into EFI pagetables

[Matt Fleming]

From: Jiri Kosina <jkosina-AlSwsSmVLrQ@public.gmane.org>

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.

Reported-by: Hanka Pavlikova <hanka-+ZI9xUNit7I@public.gmane.org>
Signed-off-by: Jiri Kosina <jkosina-AlSwsSmVLrQ@public.gmane.org>
Cc: stable-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org # v4.8+
Cc: Waiman Long <waiman.long-ZPxbGqLxI0U@public.gmane.org>
Cc: Borislav Petkov <bp-l3A5Bk7waGM@public.gmane.org>
Cc: Laura Abbott <labbott-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Vojtech Pavlik <vojtech-+ZI9xUNit7I@public.gmane.org>
Cc: Borislav Petkov <bp-Gina5bIWoIWzQB+pC5nmwQ@public.gmane.org>
Cc: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Fixes: 129766708 ("x86/efi: Only map RAM into EFI page tables if in mixed-mode")
Signed-off-by: Matt Fleming <matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org>
---
 arch/x86/platform/efi/efi_64.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 319148bd4b05..79c21cac1133 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -269,6 +269,22 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 	efi_scratch.use_pgd = true;
 
 	/*
+	 * Certain firmware versions are way too sentimential and still believe
+	 * they are exclusive and unquestionable owners of first physical page
+	 * even though they explicitly mark it as EFI_CONVENTIONAL_MEMORY
+	 * (but then write-access it later during SetVirtualAddressMap()).
+	 *
+	 * Create 1:1 mapping for this page to avoid triple faults during early
+	 * boot with such firmware. We're on a safe side, as trim_bios_range()
+	 * will reserve the first page and isolate it away from memory
+	 * allocators anyway.
+	 */
+	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
-- 
2.10.0

[tip:efi/urgent] x86/efi: Always map the first physical page into the EFI pagetables

[tip-bot for Jiri Kosina]

Commit-ID:  bf29bddf0417a4783da3b24e8c9e017ac649326f
Gitweb:     http://git.kernel.org/tip/bf29bddf0417a4783da3b24e8c9e017ac649326f
Author:     Jiri Kosina <jkosina@suse.cz>
AuthorDate: Fri, 27 Jan 2017 22:25:52 +0000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 28 Jan 2017 09:18:56 +0100

x86/efi: Always map the first physical page into the EFI pagetables

Commit:

  129766708 ("x86/efi: Only map RAM into EFI page tables if in mixed-mode")

stopped creating 1:1 mappings for all RAM, when running in native 64-bit mode.

It turns out though that there are 64-bit EFI implementations in the wild
(this particular problem has been reported on a Lenovo Yoga 710-11IKB),
which still make use of the 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 the EFI pagetables,
as soon as firmware tries to make use of it, a triple fault occurs and the
system reboots (in case of the Yoga 710-11IKB this is very early during bootup).

Fix that by always mapping the first page of physical memory into the EFI
pagetables. We're free to hand this page to the BIOS, as trim_bios_range()
will reserve the first page and isolate it away from memory allocators anyway.

Note that just reverting 129766708 alone is not enough on v4.9-rc1+ to fix the
regression on affected hardware, as this commit:

   ab72a27da ("x86/efi: Consolidate region mapping logic")

later made the first physical frame not to be mapped anyway.

Reported-by: Hanka Pavlikova <hanka@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vojtech Pavlik <vojtech@ucw.cz>
Cc: Waiman Long <waiman.long@hpe.com>
Cc: linux-efi@vger.kernel.org
Cc: stable@kernel.org # v4.8+
Fixes: 129766708 ("x86/efi: Only map RAM into EFI page tables if in mixed-mode")
Link: http://lkml.kernel.org/r/20170127222552.22336-1-matt@codeblueprint.co.uk
[ Tidied up the changelog and the comment. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/platform/efi/efi_64.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 319148b..2f25a36 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -269,6 +269,22 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 	efi_scratch.use_pgd = true;
 
 	/*
+	 * Certain firmware versions are way too sentimential and still believe
+	 * they are exclusive and unquestionable owners of the first physical page,
+	 * even though they explicitly mark it as EFI_CONVENTIONAL_MEMORY
+	 * (but then write-access it later during SetVirtualAddressMap()).
+	 *
+	 * Create a 1:1 mapping for this page, to avoid triple faults during early
+	 * boot with such firmware. We are free to hand this page to the BIOS,
+	 * as trim_bios_range() will reserve the first page and isolate it away
+	 * from memory allocators anyway.
+	 */
+	if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, _PAGE_RW)) {
+		pr_err("Failed to create 1:1 mapping for the 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

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

[Matt Fleming]

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 <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 (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: 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 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.

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

[Borislav Petkov]

On Wed, Jan 25, 2017 at 09:31:53PM +0100, 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 <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 (which is 
> > what legacy BIOS used to do, but EFI specification doesn't grant any such 
> > right to EFI BIOS ... oh well).

And now the same rant for the wider audience:

What is this EFI spec even? Toilet paper? Perhaps not even that.

Geez, can we simply say, firmware people, you f*cked up big time. Now
take all that crap with you to your basement, *think* hard about all the
issues we've had and then reengineer the whole thing from the beginning.
Completely anew. Then come back and we can talk.

There's a reason I don't want to deal with that major stinking pile of
crap called firmware but somehow I always get sucked back in.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

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

[Borislav Petkov]

On Wed, Jan 25, 2017 at 09:31:53PM +0100, 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 <jkosina-AlSwsSmVLrQ@public.gmane.org>
> > 
> > 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).

And now the same rant for the wider audience:

What is this EFI spec even? Toilet paper? Perhaps not even that.

Geez, can we simply say, firmware people, you f*cked up big time. Now
take all that crap with you to your basement, *think* hard about all the
issues we've had and then reengineer the whole thing from the beginning.
Completely anew. Then come back and we can talk.

There's a reason I don't want to deal with that major stinking pile of
crap called firmware but somehow I always get sucked back in.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
-- 

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

[Jiri Kosina]

[ 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@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 (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@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 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

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

[Jiri Kosina]

[ 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-AlSwsSmVLrQ@public.gmane.org>
> 
> 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-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org # v4.8+
> Cc: Waiman Long <waiman.long-ZPxbGqLxI0U@public.gmane.org>
> Cc: Borislav Petkov <bp-l3A5Bk7waGM@public.gmane.org>
> Cc: Laura Abbott <labbott-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Cc: Vojtech Pavlik <vojtech-+ZI9xUNit7I@public.gmane.org>
> Reported-by: Hanka Pavlikova <hanka-+ZI9xUNit7I@public.gmane.org>
> Signed-off-by: Jiri Kosina <jkosina-AlSwsSmVLrQ@public.gmane.org>
> ---
> 
> 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