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From: Wei Wang <wei.w.wang@intel.com>
To: Jim Mattson <jmattson@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	"kvm list" <kvm@vger.kernel.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Andi Kleen" <ak@linux.intel.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Kan Liang" <kan.liang@intel.com>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	like.xu@intel.com, "Jann Horn" <jannh@google.com>,
	arei.gonglei@huawei.com
Subject: Re: [PATCH v4 05/10] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest
Date: Mon, 07 Jan 2019 17:15:13 +0800	[thread overview]
Message-ID: <5C3318A1.9090009@intel.com> (raw)
In-Reply-To: <CALMp9eQ0nzKBP7az72G+eRe8C4KQQUBdj+7oD_WJHSFfYkj+Vw@mail.gmail.com>

On 01/03/2019 11:25 PM, Jim Mattson wrote:
> On Wed, Jan 2, 2019 at 11:55 PM Wei Wang <wei.w.wang@intel.com> wrote:
>
>> Right, thanks. Probably better to change it to below:
>>
>> msr_info->data = 0;
>> data = native_read_msr(MSR_IA32_PERF_CAPABILITIES);
>> if (vcpu->kvm->arch.lbr_in_guest)
>>       msr_info->data |= (data & X86_PERF_CAP_MASK_LBR_FMT);
>>
> This still breaks backwards compatibility. Returning 0 and raising #GP
> are not the same.

I'm not sure about raising GP# in this case.

This PERF_CAP msr contains more things than the lbr format.
For example, a guest with lbr=false option could read it to get PEBS_FMT,
which is PERF_CAP[11:8]. We should offer those bits in this case.

When lbr=false, the lbr feature is not usable by the guest,
so I think whatever value (0 or other value) of the LBR_FMT bits that
we give to the guest might not be important.

Best,
Wei

  reply	other threads:[~2019-01-07  9:09 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-26  9:25 [PATCH v4 00/10] Guest LBR Enabling Wei Wang
2018-12-26  9:25 ` [PATCH v4 01/10] perf/x86: fix the variable type of the LBR MSRs Wei Wang
2018-12-26  9:25 ` [PATCH v4 02/10] perf/x86: add a function to get the lbr stack Wei Wang
2018-12-26  9:25 ` [PATCH v4 03/10] KVM/x86: KVM_CAP_X86_GUEST_LBR Wei Wang
2018-12-26  9:25 ` [PATCH v4 04/10] KVM/x86: intel_pmu_lbr_enable Wei Wang
2019-01-02 16:33   ` Liang, Kan
2019-01-04  9:58     ` Wei Wang
2019-01-04 15:57       ` Liang, Kan
2019-01-05 10:09         ` Wei Wang
2019-01-07 14:22           ` Liang, Kan
2019-01-08  6:13             ` Wei Wang
2019-01-08 14:08               ` Liang, Kan
2019-01-09  1:54                 ` Wei Wang
2019-01-02 23:26   ` Jim Mattson
2019-01-03  7:22     ` Wei Wang
2019-01-03 15:34       ` Jim Mattson
2019-01-03 17:18         ` Andi Kleen
2019-01-04 10:09         ` Wei Wang
2019-01-04 15:53           ` Jim Mattson
2019-01-05 10:15             ` Wang, Wei W
2018-12-26  9:25 ` [PATCH v4 05/10] KVM/x86: expose MSR_IA32_PERF_CAPABILITIES to the guest Wei Wang
2019-01-02 23:40   ` Jim Mattson
2019-01-03  8:00     ` Wei Wang
2019-01-03 15:25       ` Jim Mattson
2019-01-07  9:15         ` Wei Wang [this message]
2019-01-07 18:05           ` Jim Mattson
2019-01-07 18:20             ` Andi Kleen
2019-01-07 18:48               ` Jim Mattson
2019-01-07 20:14                 ` Andi Kleen
2019-01-07 21:00                   ` Jim Mattson
2019-01-08  7:53                 ` Wei Wang
2019-01-08 17:19                   ` Jim Mattson
2018-12-26  9:25 ` [PATCH v4 06/10] perf/x86: no counter allocation support Wei Wang
2018-12-26  9:25 ` [PATCH v4 07/10] KVM/x86/vPMU: Add APIs to support host save/restore the guest lbr stack Wei Wang
2018-12-26  9:25 ` [PATCH v4 08/10] perf/x86: save/restore LBR_SELECT on vCPU switching Wei Wang
2018-12-26  9:25 ` [PATCH v4 09/10] perf/x86: function to check lbr user callstack mode Wei Wang
2018-12-26  9:25 ` [PATCH v4 10/10] KVM/x86/lbr: lazy save the guest lbr stack Wei Wang
2018-12-27 20:51   ` Andi Kleen
2018-12-28  3:47     ` Wei Wang
2018-12-28 19:10       ` Andi Kleen
2018-12-27 20:52   ` [PATCH v4 10/10] KVM/x86/lbr: lazy save the guest lbr stack II Andi Kleen
2018-12-29  4:25     ` Wang, Wei W

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