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

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Message-ID: <3c3115a6-f516-4f5f-8998-dafc343c829e@suse.com>
Date: Fri, 11 Apr 2025 09:46:15 +0200
From: Juergen Gross <jgross@...e.com>
To: 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>
Cc: Ingo Molnar <mingo@...nel.org>, xen-devel@...ts.xenproject.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/xen: Fix __xen_hypercall_setfunc

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>

Juergen

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