From: "Huang, Kai" <kai.huang@intel.com>
To: "thomas.lendacky@amd.com" <thomas.lendacky@amd.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"pbonzini@redhat.com" <pbonzini@redhat.com>
Cc: "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH v2] KVM: x86: use CPUID to locate host page table reserved bits
Date: Wed, 11 Dec 2019 23:16:41 +0000 [thread overview]
Message-ID: <86bb95b84a0006fbce49201d5c37f997714884ed.camel@intel.com> (raw)
In-Reply-To: <4faef0e9-72aa-9328-9110-fc67b2580f91@amd.com>
On Wed, 2019-12-11 at 14:48 -0600, Tom Lendacky wrote:
> On 12/11/19 3:07 AM, Paolo Bonzini wrote:
> > On 11/12/19 01:11, Huang, Kai wrote:
> > > > kvm_get_shadow_phys_bits() must be conservative in that:
> > > >
> > > > 1) if a bit is reserved it _can_ return a value higher than its index
> > > >
> > > > 2) if a bit is used by the processor (for physical address or anything
> > > > else) it _must_ return a value higher than its index.
> > > >
> > > > In the SEV case we're not obeying (2), because the function returns 43
> > > > when the C bit is bit 47. The patch fixes that.
> > > Could we guarantee that C-bit is always below bits reported by CPUID?
> >
> > That's a question for AMD. :) The C bit can move (and probably will,
> > otherwise they wouldn't have bothered adding it to CPUID) in future
> > generations of the processor.
>
> Right, there's no way to guarantee that it is always below bits reported
> by CPUID. As Paolo stated, the position is reported by CPUID so that it
> can easily move and be accounted for programmatically.
Then I don't think this patch could fix the issue Paolo discribed?
Thanks,
-Kai
prev parent reply other threads:[~2019-12-11 23:16 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-04 15:40 [PATCH v2] KVM: x86: use CPUID to locate host page table reserved bits Paolo Bonzini
2019-12-04 15:48 ` Sean Christopherson
2019-12-10 9:19 ` Paolo Bonzini
2019-12-10 15:37 ` Sean Christopherson
2019-12-04 15:57 ` Tom Lendacky
2019-12-10 3:53 ` Huang, Kai
2019-12-10 9:18 ` Paolo Bonzini
2019-12-10 9:17 ` Paolo Bonzini
2019-12-11 0:11 ` Huang, Kai
2019-12-11 9:07 ` Paolo Bonzini
2019-12-11 20:48 ` Tom Lendacky
2019-12-11 23:16 ` Huang, Kai [this message]
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