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

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Message-ID: <ff39455a-7fa8-48c1-ba43-33ea4992f6e1@suse.com>
Date: Fri, 11 Apr 2025 11:29:47 +0200
From: Jürgen Groß <jgross@...e.com>
To: Ingo Molnar <mingo@...nel.org>
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

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.

Juergen

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