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Message-ID: <cbbdb23f-4261-4f48-4143-c5fb6c78da06@intel.com>
Date: Thu, 29 Dec 2022 15:02:55 +0800
From: "Yang, Weijiang" <weijiang.yang@...el.com>
To: "Zhang, Chen" <chen.zhang@...el.com>
CC: "Gao, Chao" <chao.gao@...el.com>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>,
"Christopherson,, Sean" <seanjc@...gle.com>,
"H. Peter Anvin" <hpa@...or.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
"x86@...nel.org" <x86@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH 6/9] kvm/x86: Add ARCH_CAP_VIRTUAL_ENUM for guest
MSR_IA32_ARCH_CAPABILITIES
On 12/29/2022 10:58 AM, Zhang, Chen wrote:
[...]
>> \
>>> + ARCH_CAP_VIRTUAL_ENUM)
>>>
>>> static u64 kvm_get_arch_capabilities(void)
>>> {
>>> @@ -1607,6 +1611,13 @@ static u64 kvm_get_arch_capabilities(void)
>>> */
>>> data |= ARCH_CAP_PSCHANGE_MC_NO;
>>>
>>> + /*
>>> + * Virtual MSRs can allow guests to notify VMM whether or not
>>> + * they are using specific software mitigation, allowing a VMM
>>> + * to enable there hardware control only where necessary.
>>> + */
>>> + data |= ARCH_CAP_VIRTUAL_ENUM;
>>
>> IMO, this is: data &= ARCH_CAP_VIRTUAL_ENUM; because it requires
>> platform support.
> Intel defined the virtual MSRs for software mitigations for all platforms.
> KVM should be unconditionally opened it for the software mitigation in migration pools.
> For example migration from the old platform to the new platform.
> Please check the Software Mitigations in Migration Pools section in documents:
> https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/branch-history-injection.html
If this series running on old platforms, how VMM can set specific vmcs
fields,
e.g., “virtualize IA32_SPEC_CTRL” VM-execution control, to mitigate
guest issues?
>
>>
>>> +
>>> /*
>>> * If we're doing cache flushes (either "always" or "cond")
>>> * we will do one whenever the guest does a vmlaunch/vmresume.
>>> @@ -1657,6 +1668,9 @@ static int kvm_get_msr_feature(struct
>> kvm_msr_entry *msr)
>>> case MSR_IA32_UCODE_REV:
>>> rdmsrl_safe(msr->index, &msr->data);
>>> break;
>>> + case MSR_VIRTUAL_ENUMERATION:
>>> + msr->data = VIRT_ENUM_MITIGATION_CTRL_SUPPORT;
>>
>> Need to check bit 63 of host MSR_ARCH_CAPABILITIES before expose the
>> feature.
> Refer to the above comments.
>
> Thanks
> Chen
>
>>
>>> + break;
>>> default:
>>> return static_call(kvm_x86_get_msr_feature)(msr);
>>> }
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