linux-kernel - Re: [PATCHv3 06/14] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

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Date:   Wed, 15 Nov 2023 16:03:06 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>,
        kexec@...ts.infradead.org, linux-coco@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 06/14] x86/kexec: Keep CR4.MCE set during kexec for TDX
 guest

On Wed, Nov 15, 2023 at 01:23:43PM +0100, Peter Zijlstra wrote:
> On Wed, Nov 15, 2023 at 03:00:36PM +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@...ux.intel.com>
> > Reviewed-by: Kai Huang <kai.huang@...el.com>
> > ---
> >  arch/x86/kernel/relocate_kernel_64.S | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
> > index 56cab1bb25f5..bea89814b48e 100644
> > --- a/arch/x86/kernel/relocate_kernel_64.S
> > +++ b/arch/x86/kernel/relocate_kernel_64.S
> > @@ -145,11 +145,16 @@ 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 "jmp 1f", "", X86_FEATURE_TDX_GUEST
> > +	orl	$X86_CR4_MCE, %eax
> >  1:
> 
> 	ALTERNATIVE "", "orl $X86_CR4_MCE, %eax", X86_FEATURE_TDX_GUEST
> 
> ?

Oh. Right. Silly me.

Will fix.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov