linux-kernel - Re: [PATCH] x86/xen: Fix __xen_hypercall

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Message-ID: <Z_jgauFyTTKgVnJy@gmail.com>
Date: Fri, 11 Apr 2025 11:27:06 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Juergen Gross <jgross@...e.com>
Cc: Jason Andryuk <jason.andryuk@....com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	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,
	"H. Peter Anvin" <hpa@...or.com>, "Xin Li (Intel)" <xin@...or.com>,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/xen: Fix __xen_hypercall_setfunc


* Juergen Gross <jgross@...e.com> wrote:

> On 10.04.25 21:31, Jason Andryuk wrote:
> > Hypercall detection is failing with xen_hypercall_intel() chosen even on
> > an AMD processor.  Looking at the disassembly, the call to
> > xen_get_vendor() was removed.
> > 
> > The check for boot_cpu_has(X86_FEATURE_CPUID) was used as a proxy for
> > the x86_vendor having been set.  When
> > CONFIG_X86_REQUIRED_FEATURE_CPUID=y (the default value), DCE eliminates
> > the call to xen_get_vendor().  An uninitialized value 0 means
> > X86_VENDOR_INTEL, so the Intel function is always returned.
> > 
> > Remove the if and always call xen_get_vendor() to avoid this issue.
> > 
> > Fixes: 3d37d9396eb3 ("x86/cpufeatures: Add {REQUIRED,DISABLED} feature configs")
> > Suggested-by: Juergen Gross <jgross@...e.com>
> > Signed-off-by: Jason Andryuk <jason.andryuk@....com>
> 
> Reviewed-by: Juergen Gross <jgross@...e.com>

Wanna merge this via the Xen tree, or should it go to x86/urgent?

The bug was *caused* by the x86 tree so we'd be glad to merge,
but your call.

If you'll merge it:

  Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo