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From: Paolo Bonzini <pbonzini@redhat.com>
To: Yang Weijiang <weijiang.yang@intel.com>
Cc: rkrcmar@redhat.com, sean.j.christopherson@intel.com,
	jmattson@google.com, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, mst@redhat.com, yu-cheng.yu@intel.com,
	yi.z.zhang@intel.com, hjl.tools@gmail.com,
	Zhang Yi Z <yi.z.zhang@linux.intel.com>
Subject: Re: [PATCH v2 1/7] KVM:VMX: Define CET VMCS fields and bits
Date: Wed, 30 Jan 2019 09:32:59 +0100	[thread overview]
Message-ID: <e80bd3f5-7276-6c2a-3ad9-3ce0d0d0bff7@redhat.com> (raw)
In-Reply-To: <20190129082917.GA32725@local-michael-cet-test.sh.intel.com>

On 29/01/19 09:29, Yang Weijiang wrote:
> On Tue, Jan 29, 2019 at 04:19:34PM +0100, Paolo Bonzini wrote:
>> On 28/01/19 11:33, Yang Weijiang wrote:
>>>> There is no code in this series to pass these fields to and from
>>>> userspace, and also to save/restore U_CET, INT_SSP_TAB, PL0_SSP and
>>>> PL3_SSP across context switches.
>>>>
>>> The kernel consumes these MSRs, please see kernel CET patch:
>>> https://lkml.org/lkml/fancy/2018/11/20/225
>>
>> Still, even if the kernel saves these fields across context switch in
>> XSAVE areas, KVM must support accesses to the MSRs from userspace, for
>> example in order to perform live migration.
>>
>> For example, when reading/writing these in kvm_set_msr or
>> kvm_get_msr_common, you would have to do a read/write from the host
>> MSRs.  You also have to put kvm_load_guest_fpu/kvm_put_guest_fpu calls
>> in __msr_io.
> Thanks, you're right, if we want to support live migration we need do that.
> However, this feature relies on quite a few external
> dependencies, e.g., cpu capabilities, kernel version and configuration, we
> don't support live migration right now. what's your opinion?

Live migration is generally a requirement for a feature to be accepted
in KVM.

Paolo

>> Thanks,
>>
>> Paolo
>>
>>>> In addition, PL1_SSP and PL2_SSP should be supported even if the guest
>>>> doesn't use them.  It makes sense to avoid intercepting them, but they
>>>> should still be supported and switched (possibly only if nonzero).
>>>>
>>>> Am I missing something, for example a dependency on host CET support?
>>>> If not, how was this series tested?
>>>>
>>> The guest CET feature is tested with kernel CET patches on internal
>>> virtual platform.
>>>


  reply	other threads:[~2019-01-30  8:33 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-22 20:59 [PATCH v2 0/7] This patch-set is to enable Guest CET support Yang Weijiang
2019-01-22 20:59 ` [PATCH v2 1/7] KVM:VMX: Define CET VMCS fields and bits Yang Weijiang
2019-01-25 18:02   ` Paolo Bonzini
2019-01-28 10:33     ` Yang Weijiang
2019-01-29 15:19       ` Paolo Bonzini
2019-01-29  8:29         ` Yang Weijiang
2019-01-30  8:32           ` Paolo Bonzini [this message]
2019-03-04 18:56         ` Sean Christopherson
2019-03-08  9:15           ` Paolo Bonzini
2019-03-08 15:50             ` Sean Christopherson
2019-03-08 16:34               ` Paolo Bonzini
2019-01-25 22:30   ` Sean Christopherson
2019-01-29 17:47   ` Jim Mattson
2019-01-29 18:01     ` Jim Mattson
     [not found]       ` <20190129182750.GB8156@linux.intel.com>
2019-01-29  8:34         ` Yang Weijiang
2019-01-22 20:59 ` [PATCH v2 2/7] KVM:CPUID: Define CET CPUID bits and CR4.CET master enable bit Yang Weijiang
2019-01-22 20:59 ` [PATCH v2 3/7] KVM:CPUID: Add CPUID support for CET xsaves component query Yang Weijiang
2019-01-25 17:57   ` Paolo Bonzini
2019-01-25 22:40   ` Sean Christopherson
2019-01-22 20:59 ` [PATCH v2 4/7] KVM:CPUID: Fix xsaves area size calculation for CPUID.(EAX=0xD,ECX=1) Yang Weijiang
2019-01-25 22:47   ` Sean Christopherson
2019-01-22 20:59 ` [PATCH v2 5/7] KVM:VMX: Pass through host CET related MSRs to Guest Yang Weijiang
2019-01-25 22:50   ` Sean Christopherson
2019-01-22 20:59 ` [PATCH v2 6/7] KVM:VMX: Load Guest CET via VMCS when CET is enabled in Guest Yang Weijiang
2019-01-25 22:56   ` Sean Christopherson
2019-01-30 15:16     ` Yang Weijiang
2019-01-22 20:59 ` [PATCH v2 7/7] KVM:X86: Enable MSR_IA32_XSS bit 11 and 12 for CET xsaves/xrstors Yang Weijiang
2019-01-25 23:03   ` Sean Christopherson

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