From: Sean Christopherson <seanjc@google.com>
To: Jim Mattson <jmattson@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] KVM: x86: Reject loading KVM if host.PAT[0] != WB
Date: Fri, 15 Jul 2022 23:18:03 +0000 [thread overview]
Message-ID: <YtH1q3C4F+LAEDTf@google.com> (raw)
In-Reply-To: <CALMp9eQdzZK4ZAyQZXUWff_zuRRdr=ugkujWfFrt9dP8uFcs=Q@mail.gmail.com>
On Fri, Jul 15, 2022, Jim Mattson wrote:
> On Fri, Jul 15, 2022 at 4:02 PM Sean Christopherson <seanjc@google.com> wrote:
> >
> > Reject KVM if entry '0' in the host's IA32_PAT MSR is not programmed to
> > writeback (WB) memtype. KVM subtly relies on IA32_PAT entry '0' to be
> > programmed to WB by leaving the PAT bits in shadow paging and NPT SPTEs
> > as '0'. If something other than WB is in PAT[0], at _best_ guests will
> > suffer very poor performance, and at worst KVM will crash the system by
> > breaking cache-coherency expecations (e.g. using WC for guest memory).
> >
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> What if someone changes the host's PAT to violate this rule *after*
> kvm is loaded?
Then KVM (and probably many other things in the kernel) is hosed. The same argument
(that KVM isn't paranoid enough) can likely be made for a number of MSRs and critical
registers.
next prev parent reply other threads:[~2022-07-15 23:18 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-15 23:00 [PATCH 0/4] KVM: x86/mmu: Memtype related cleanups Sean Christopherson
2022-07-15 23:00 ` [PATCH 1/4] KVM: x86: Reject loading KVM if host.PAT[0] != WB Sean Christopherson
2022-07-15 23:06 ` Jim Mattson
2022-07-15 23:18 ` Sean Christopherson [this message]
2022-07-18 9:42 ` Maxim Levitsky
2022-07-15 23:00 ` [PATCH 2/4] KVM: x86: Drop unnecessary goto+label in kvm_arch_init() Sean Christopherson
2022-07-18 10:03 ` Maxim Levitsky
2022-07-18 15:10 ` Sean Christopherson
2022-07-15 23:00 ` [PATCH 3/4] KVM: x86/mmu: Add shadow mask for effective host MTRR memtype Sean Christopherson
2022-07-18 12:08 ` Maxim Levitsky
2022-07-18 16:07 ` Sean Christopherson
2022-07-15 23:00 ` [PATCH 4/4] KVM: x86/mmu: Restrict mapping level based on guest MTRR iff they're used Sean Christopherson
2022-07-18 12:08 ` Maxim Levitsky
2022-07-19 17:59 ` [PATCH 0/4] KVM: x86/mmu: Memtype related cleanups Paolo Bonzini
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