Re: [PATCH] x86emul: don't read mask register on AVX512F-incapable platforms

From: Andrew Cooper <andrew.cooper3@citrix.com>
To: George Dunlap <george.dunlap@citrix.com>,
	Jan Beulich <JBeulich@suse.com>,
	xen-devel <xen-devel@lists.xenproject.org>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>,
	Juergen Gross <jgross@suse.com>, Wei Liu <wei.liu2@citrix.com>,
	Roger Pau Monne <roger.pau@citrix.com>
Subject: Re: [PATCH] x86emul: don't read mask register on AVX512F-incapable platforms
Date: Thu, 28 Mar 2019 18:03:40 +0000	[thread overview]
Message-ID: <baef5f45-98ca-a53b-daac-6c0f7884eb26@citrix.com> (raw)
In-Reply-To: <232d7494-4976-4028-4cef-76f9bef85981@citrix.com>

On 28/03/2019 17:44, George Dunlap wrote:
> On 3/28/19 5:03 PM, Jan Beulich wrote:
>> Reported-by: George Dunlap <george.dunlap@citrix.com>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> That seems to fix all the ones related to the crashes I was seeing:
>
> Tested-by: George Dunlap <george.dunlap@citrix.com>
>
>> ---
>> This is surely a stable tree candidate, unless it could still make it
>> into 4.12 before the release.
>>
>> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
>> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
>> @@ -3511,7 +3511,7 @@ x86_emulate(
>>      }
>>  
>>      /* With a memory operand, fetch the mask register in use (if any). */
>> -    if ( ea.type == OP_MEM && evex.opmsk )
>> +    if ( ea.type == OP_MEM && cpu_has_avx512f && evex.opmsk )

So, this certainly will fix the crash as reported, you need an %xcr0
check, to prevent other ways of this stub faulting.

~Andrew

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