From: Xiaoyao Li <xiaoyao.li@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: jmattson@google.com,
Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [PATCH] kvm: x86: Use KVM CPU capabilities to determine CR4 reserved bits
Date: Mon, 18 May 2020 12:52:30 +0800 [thread overview]
Message-ID: <6a4daca4-6034-901a-261f-215df7d606a6@intel.com> (raw)
In-Reply-To: <20200506094436.3202-1-pbonzini@redhat.com>
On 5/6/2020 5:44 PM, Paolo Bonzini wrote:
> Using CPUID data can be useful for the processor compatibility
> check, but that's it. Using it to compute guest-reserved bits
> can have both false positives (such as LA57 and UMIP which we
> are already handling) and false negatives:
> in particular, with
> this patch we don't allow anymore a KVM guest to set CR4.PKE
> when CR4.PKE is clear on the host.
A common question about whether a feature can be exposed to guest:
Given a feature, there is a CPUID bit to enumerate it, and a CR4 bit to
turn it on/off. Whether the feature can be exposed to guest only depends
on host CR4 setting? I.e., if CPUID bit is not cleared in cpu_data in
host but host kernel doesn't set the corresponding CR4 bit to turn it
on, we cannot expose the feature to guest. right?
next prev parent reply other threads:[~2020-05-18 4:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 9:44 [PATCH] kvm: x86: Use KVM CPU capabilities to determine CR4 reserved bits Paolo Bonzini
2020-05-18 4:52 ` Xiaoyao Li [this message]
2020-05-18 12:31 ` Paolo Bonzini
2020-05-18 15:49 ` Xiaoyao Li
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