diff mbox series

[PATCHv4,06/14] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

Message ID 20231205004510.27164-7-kirill.shutemov@linux.intel.com
State New
Headers
Series x86/tdx: Add kexec support |

Commit Message

Kirill A. Shutemov Dec. 5, 2023, 12:45 a.m. UTC 
  TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
to #VE.

Use alternatives to keep the flag during kexec for TDX guests.

The change doesn't affect non-TDX-guest environments.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
---
 arch/x86/kernel/relocate_kernel_64.S | 3 +++
 1 file changed, 3 insertions(+)

Comments

Kai Huang Dec. 5, 2023, 11:58 p.m. UTC | #1 
On Tue, 2023-12-05 at 03:45 +0300, Kirill A. Shutemov wrote:
> TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
> to #VE.
> 
> Use alternatives to keep the flag during kexec for TDX guests.
> 
> The change doesn't affect non-TDX-guest environments.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Kai Huang <kai.huang@intel.com>
> ---
>  arch/x86/kernel/relocate_kernel_64.S | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
> index 56cab1bb25f5..cd6a53667c6b 100644
> --- a/arch/x86/kernel/relocate_kernel_64.S
> +++ b/arch/x86/kernel/relocate_kernel_64.S
> @@ -145,12 +145,15 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
>  	 * Set cr4 to a known state:
>  	 *  - physical address extension enabled
>  	 *  - 5-level paging, if it was enabled before
> +	 *  - Machine check exception on TDX guest. Clearing MCE is not allowed
> +	 *    in TDX guests.
>  	 */
>  	movl	$X86_CR4_PAE, %eax
>  	testq	$X86_CR4_LA57, %r13
>  	jz	1f
>  	orl	$X86_CR4_LA57, %eax
>  1:
> +	ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST
>  	movq	%rax, %cr4
>  
>  	jmp 1f

Nit:

It seems <asm/alternative.h> isn't included in relocate_kernel_64.S.  Maybe it's
better to do it explicitly.

Maybe even better to explicitly include <linux/stringify.h> too, but I see
<asm/alternative.h> already does that.
Kirill A. Shutemov Dec. 6, 2023, 1:26 p.m. UTC | #2 
On Tue, Dec 05, 2023 at 11:58:45PM +0000, Huang, Kai wrote:
> On Tue, 2023-12-05 at 03:45 +0300, Kirill A. Shutemov wrote:
> > TDX guests are not allowed to clear CR4.MCE. Attempt to clear it leads
> > to #VE.
> > 
> > Use alternatives to keep the flag during kexec for TDX guests.
> > 
> > The change doesn't affect non-TDX-guest environments.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Reviewed-by: Kai Huang <kai.huang@intel.com>
> > ---
> >  arch/x86/kernel/relocate_kernel_64.S | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
> > index 56cab1bb25f5..cd6a53667c6b 100644
> > --- a/arch/x86/kernel/relocate_kernel_64.S
> > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > @@ -145,12 +145,15 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
> >  	 * Set cr4 to a known state:
> >  	 *  - physical address extension enabled
> >  	 *  - 5-level paging, if it was enabled before
> > +	 *  - Machine check exception on TDX guest. Clearing MCE is not allowed
> > +	 *    in TDX guests.
> >  	 */
> >  	movl	$X86_CR4_PAE, %eax
> >  	testq	$X86_CR4_LA57, %r13
> >  	jz	1f
> >  	orl	$X86_CR4_LA57, %eax
> >  1:
> > +	ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST
> >  	movq	%rax, %cr4
> >  
> >  	jmp 1f
> 
> Nit:
> 
> It seems <asm/alternative.h> isn't included in relocate_kernel_64.S.  Maybe it's
> better to do it explicitly.
> 
> Maybe even better to explicitly include <linux/stringify.h> too, but I see
> <asm/alternative.h> already does that.

Okay, I will add both.
diff mbox series

Patch

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 56cab1bb25f5..cd6a53667c6b 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -145,12 +145,15 @@  SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	 * Set cr4 to a known state:
 	 *  - physical address extension enabled
 	 *  - 5-level paging, if it was enabled before
+	 *  - Machine check exception on TDX guest. Clearing MCE is not allowed
+	 *    in TDX guests.
 	 */
 	movl	$X86_CR4_PAE, %eax
 	testq	$X86_CR4_LA57, %r13
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
 1:
+	ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST
 	movq	%rax, %cr4
 
 	jmp 1f