From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v13 for-xen-4.5 17/21] x86/VPMU: Handle PMU
 interrupts for PV guests
Date: Mon, 13 Oct 2014 15:10:38 -0400
Message-ID: <543C23AE.6000305@oracle.com>
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To: Jan Beulich <JBeulich@suse.com>
Cc: kevin.tian@intel.com, keir@xen.org, suravee.suthikulpanit@amd.com, andrew.cooper3@citrix.com, tim@xen.org, dietmar.hahn@ts.fujitsu.com, xen-devel@lists.xen.org, Aravind.Gopalakrishnan@amd.com, jun.nakajima@intel.com, dgdegra@tycho.nsa.gov
List-Id: xen-devel@lists.xenproject.org

On 10/13/2014 11:29 AM, Jan Beulich wrote:
>>>> On 03.10.14 at 23:40, <boris.ostrovsky@oracle.com> wrote:
>>   int vpmu_do_wrmsr(unsigned int msr, uint64_t msr_content, uint64_t supported)
>>   {
>> -    struct vpmu_struct *vpmu = vcpu_vpmu(current);
>> +    struct vcpu *curr = current;
>> +    struct vpmu_struct *vpmu = vcpu_vpmu(curr);
>>   
>>       if ( !(vpmu_mode & (XENPMU_MODE_SELF | XENPMU_MODE_HV)) )
>>           return 0;
>>   
>>       if ( vpmu->arch_vpmu_ops && vpmu->arch_vpmu_ops->do_wrmsr )
>> -        return vpmu->arch_vpmu_ops->do_wrmsr(msr, msr_content, supported);
>> +    {
>> +        int ret = vpmu->arch_vpmu_ops->do_wrmsr(msr, msr_content, supported);
>> +
>> +        /*
>> +         * We may have received a PMU interrupt during WRMSR handling
>> +         * and since do_wrmsr may load VPMU context we should save
>> +         * (and unload) it again.
>> +         */
> Is this btw true also when do_wrmsr() failed? Or could you not rather
> handle ret != 0 before the following if() (or check ret == 0 together
> with the other conditions)?

There is indeed no need to save/unload if do_wrmsr() failed but one of 
conditions in the if() that you refer to (PMU_CACHED bit test) can only 
happen if do_wrmsr() succeeded because the context could not have been 
loaded in case of failure.

-boris