[v1] x86/kexec: Fixes for tip/x86/boot

[PATCH 2/9] x86/kexec: Ensure preserve_context flag is set on return to kernel

Posted by David Woodhouse 1 year ago

From: David Woodhouse <dwmw@amazon.co.uk>

The swap_pages function will only actually *swap*, as its name implies,
if the preserve_context flag in the %r11 register is non-zero. On the
way back from a ::preserve_context kexec, ensure that the %r11 register
is non-zero so that the pages get swapped back.

Fixes: 9e5683e2d0b5 ("x86/kexec: Only swap pages for ::preserve_context mode")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
 arch/x86/kernel/relocate_kernel_64.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 9bd601dd8659..1a52e4339c1d 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -220,6 +220,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	movq	kexec_pa_table_page(%rip), %rax
 	movq	%rax, %cr3
 	lea	PAGE_SIZE(%r8), %rsp
+	movq	$1, %r11	/* Ensure preserve_context flag is set */
 	call	swap_pages
 	movq	kexec_va_control_page(%rip), %rax
 	addq	$(virtual_mapped - relocate_kernel), %rax
-- 
2.47.0

Re: [PATCH 2/9] x86/kexec: Ensure preserve_context flag is set on return to kernel

Posted by Uros Bizjak 1 year ago


On 17. 12. 24 00:24, David Woodhouse wrote:
> From: David Woodhouse <dwmw@amazon.co.uk>
> 
> The swap_pages function will only actually *swap*, as its name implies,
> if the preserve_context flag in the %r11 register is non-zero. On the
> way back from a ::preserve_context kexec, ensure that the %r11 register
> is non-zero so that the pages get swapped back.
> 
> Fixes: 9e5683e2d0b5 ("x86/kexec: Only swap pages for ::preserve_context mode")
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>   arch/x86/kernel/relocate_kernel_64.S | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
> index 9bd601dd8659..1a52e4339c1d 100644
> --- a/arch/x86/kernel/relocate_kernel_64.S
> +++ b/arch/x86/kernel/relocate_kernel_64.S
> @@ -220,6 +220,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
>   	movq	kexec_pa_table_page(%rip), %rax
>   	movq	%rax, %cr3
>   	lea	PAGE_SIZE(%r8), %rsp
> +	movq	$1, %r11	/* Ensure preserve_context flag is set */

You can save a byte here by using "movl $1, %r11d".

>   	call	swap_pages
>   	movq	kexec_va_control_page(%rip), %rax
>   	addq	$(virtual_mapped - relocate_kernel), %rax

Uros.

Re: [PATCH 2/9] x86/kexec: Ensure preserve_context flag is set on return to kernel

Posted by David Woodhouse 11 months, 2 weeks ago

On Tue, 2024-12-17 at 17:38 +0100, Uros Bizjak wrote:
>  
> > diff --git a/arch/x86/kernel/relocate_kernel_64.S
> > b/arch/x86/kernel/relocate_kernel_64.S
> > index 9bd601dd8659..1a52e4339c1d 100644
> > --- a/arch/x86/kernel/relocate_kernel_64.S
> > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > @@ -220,6 +220,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
> >    	movq	kexec_pa_table_page(%rip), %rax
> >    	movq	%rax, %cr3
> >    	lea	PAGE_SIZE(%r8), %rsp
> > +	movq	$1, %r11	/* Ensure preserve_context flag is
> > set */
> 
> You can save a byte here by using "movl $1, %r11d".

Thanks. I've done that locally.