linux-kernel - Re: [PATCH v2 1/3] xen/pv: allow pmu msr accesses to cause GP

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Date:   Tue, 4 Oct 2022 17:50:44 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     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>,
        "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 1/3] xen/pv: allow pmu msr accesses to cause GP

On 04.10.2022 17:22, Juergen Gross wrote:
> On 04.10.22 12:58, Jan Beulich wrote:
>> On 04.10.2022 10:43, Juergen Gross wrote:
>>> Today pmu_msr_read() and pmu_msr_write() fall back to the safe variants
>>> of read/write MSR in case the MSR access isn't emulated via Xen. Allow
>>> the caller to select the potentially faulting variant by passing NULL
>>> for the error pointer.
>>>
>>> Restructure the code to make it more readable.
>>>
>>> Signed-off-by: Juergen Gross <jgross@...e.com>
>>
>> I think the title (and to some degree also the description) is misleading:
>> The property we care about here isn't whether an MSR access would raise
>> #GP (we can't control that), but whether that #GP would be recovered from.
> 
> Would you be fine with adding "fatal" or "visible"?

That would help, but "allow" also is a little odd when it comes to
(likely) crashing the system.

Jan