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

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Message-ID: <Z_jkZw58Ew5Iwj5K@gmail.com>
Date: Fri, 11 Apr 2025 11:44:07 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Jürgen 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


* Jürgen Groß <jgross@...e.com> wrote:

> On 11.04.25 11:27, Ingo Molnar wrote:
> > 
> > * 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.
> 
> x86/urgent is fine for me.

Applied, thanks!

	Ingo