From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>,
Yang Weijiang <weijiang.yang@intel.com>
Cc: rkrcmar@redhat.com, jmattson@google.com,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
mst@redhat.com, yu-cheng.yu@intel.com,
Zhang Yi Z <yi.z.zhang@linux.intel.com>,
wei.w.wang@intel.com, weijiang.yang@inte.com
Subject: Re: [PATCH v3 6/8] KVM:VMX: Load Guest CET via VMCS when CET is enabled in Guest
Date: Fri, 8 Mar 2019 17:36:50 +0100 [thread overview]
Message-ID: <9e80935f-b572-8210-6ea1-a582b3d05f88@redhat.com> (raw)
In-Reply-To: <20190308162835.GB2528@linux.intel.com>
On 08/03/19 17:28, Sean Christopherson wrote:
> On Mon, Mar 04, 2019 at 08:36:55PM +0800, Yang Weijiang wrote:
>> On Mon, Mar 04, 2019 at 07:12:02PM -0800, Sean Christopherson wrote:
>>> On Mon, Mar 04, 2019 at 05:56:40PM +0800, Yang Weijiang wrote:
>>>> Cannot agree with you more!
>>>> This is some design limitation, but from my point of view, once vmm
>>>> exposes CET capability to guest via CPUID, it grants the guest kernel freedom to choose
>>>> which features to be enabled, we don't need to add extra constraints on
>>>> the usage.
>>>
>>> But if KVM allows SHSTK and IBT to be toggled independently then the VMM
>>> has only exposed SHSTK or IBT, not CET as whole.
>>>
>>> Even if SHSTK and IBT are bundled together the guest still has to opt-in
>>> to enabling each feature. I don't see what we gain by pretending that
>>> SHSTK/IBT can be individually exposed to the guest, and on the flip side
>>> doing so creates a virtualization hole.
>> you almost convinced me ;-), maybe I'll make the feature as a bundle in
>> next release after check with kernel team. BTW, what do you mean by
>> saying "create a virtualization hole"? Is it what you stated in above
>> reply?
>
> By "virtualization hole" I mean the guest would be able to use a feature
> that the virtual CPU model says isn't supported.
I think it's okay to leave the hole and leave it to userspace to forbid
enabling only one of the bits.
Paolo
> After rereading the XSS architecture, there's a marginally less crappy
> option for handling XRSTOR as we could use the XSS_EXIT_BITMAP to
> intercept XRSTOR if SHSTK != IBT and the guest is restoring CET state,
> e.g. to ensure the guest isn't setting IA32_PL*_SSP if !SHSTK and isn't
> setting bits that are effectively reserved in IA32_U_CET.
>
> But practically speaking that'd be the same as intercepting XRSTORS
> unconditionally when the guest is using CET, i.e. it's still going to
> tank the performance of a guest that uses CET+XSAVES/XRSTORS.
>
next prev parent reply other threads:[~2019-03-08 16:37 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-25 13:27 [PATCH v3 0/8] This patch-set is to enable Guest CET support Yang Weijiang
2019-02-25 13:27 ` [PATCH v3 1/8] KVM:VMX: Define CET VMCS fields and bits Yang Weijiang
2019-02-26 19:31 ` Jim Mattson
2019-02-26 7:52 ` Yang Weijiang
2019-02-28 15:53 ` Sean Christopherson
2019-02-28 9:51 ` Yang Weijiang
2019-02-25 13:27 ` [PATCH v3 2/8] KVM:CPUID: Define CET CPUID bits and CR4.CET master enable bit Yang Weijiang
2019-02-26 19:48 ` Jim Mattson
2019-02-26 7:57 ` Yang Weijiang
2019-03-01 2:15 ` Xiaoyao Li
2019-02-28 16:04 ` Sean Christopherson
2019-02-28 8:10 ` Yang Weijiang
2019-02-25 13:27 ` [PATCH v3 3/8] KVM:CPUID: Add CPUID support for Guest CET Yang Weijiang
2019-02-28 15:59 ` Sean Christopherson
2019-02-28 8:28 ` Yang Weijiang
2019-03-01 14:53 ` Sean Christopherson
2019-03-03 9:36 ` Yang Weijiang
2019-03-04 18:28 ` Sean Christopherson
2019-03-04 12:17 ` Yang Weijiang
2019-03-04 18:47 ` Sean Christopherson
2019-03-04 10:01 ` Yang Weijiang
2019-03-04 18:54 ` Sean Christopherson
2019-03-04 10:11 ` Yang Weijiang
2019-03-08 11:32 ` Paolo Bonzini
2019-03-10 12:18 ` Yang Weijiang
2019-02-25 13:27 ` [PATCH v3 4/8] KVM:CPUID: Fix xsaves area size calculation for CPUID.(EAX=0xD,ECX=1) Yang Weijiang
2019-02-25 13:27 ` [PATCH v3 5/8] KVM:VMX: Pass through host CET related MSRs to Guest Yang Weijiang
2019-03-04 18:53 ` Sean Christopherson
2019-03-04 10:07 ` Yang Weijiang
2019-03-05 3:21 ` Sean Christopherson
2019-02-25 13:27 ` [PATCH v3 6/8] KVM:VMX: Load Guest CET via VMCS when CET is enabled in Guest Yang Weijiang
2019-02-28 16:17 ` Sean Christopherson
2019-02-28 8:38 ` Yang Weijiang
2019-03-01 14:58 ` Sean Christopherson
2019-03-03 12:26 ` Yang Weijiang
2019-03-04 18:43 ` Sean Christopherson
2019-03-04 9:56 ` Yang Weijiang
2019-03-05 3:12 ` Sean Christopherson
2019-03-04 12:36 ` Yang Weijiang
2019-03-08 16:28 ` Sean Christopherson
2019-03-08 16:36 ` Paolo Bonzini [this message]
2019-02-25 13:27 ` [PATCH v3 7/8] KVM:X86: Add XSS bit 11 and 12 support for CET xsaves/xrstors Yang Weijiang
2019-02-28 16:25 ` Sean Christopherson
2019-02-28 8:44 ` Yang Weijiang
2019-03-08 11:32 ` Paolo Bonzini
2019-03-10 12:20 ` Yang Weijiang
2019-03-10 13:35 ` Yang Weijiang
2019-03-11 15:32 ` Paolo Bonzini
2019-03-12 14:30 ` Yang Weijiang
2019-03-08 10:49 ` Paolo Bonzini
2019-03-11 1:29 ` Kang, Luwei
2019-02-25 13:27 ` [PATCH v3 8/8] KVM:X86: Add user-space read/write interface for CET MSRs Yang Weijiang
2019-02-28 16:32 ` Sean Christopherson
2019-02-28 9:41 ` Yang Weijiang
2019-03-08 17:30 ` Sean Christopherson
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