From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
Lai Jiangshan <laijs@linux.alibaba.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 1/4] KVM: X86: Fix tlb flush for tdp in kvm_invalidate_pcid()
Date: Thu, 21 Oct 2021 19:13:02 +0200 [thread overview]
Message-ID: <945500f6-27e1-ed81-2b7d-c709cb1d4b33@redhat.com> (raw)
In-Reply-To: <YXF+pG0yGA0TQZww@google.com>
On 21/10/21 16:52, Sean Christopherson wrote:
>> I think the EPT violation happens*after* the cr3 write. So the instruction to be
>> emulated is not "cr3 write". The emulation will queue fault into guest though,
>> recursive EPT violation happens since the cr3 exceeds maxphyaddr limit.
> Doh, you're correct. I think my mind wandered into thinking about what would
> happen with PDPTRs and forgot to get back to normal MOV CR3.
>
> So yeah, the only way to correctly handle this would be to intercept CR3 loads.
> I'm guessing that would have a noticeable impact on guest performance.
Ouch... yeah, allow_smaller_maxphyaddr already has bad performance, but
intercepting CR3 loads would be another kind of slow.
Paolo
> Paolo, I'll leave this one for you to decide, we have pretty much written off
> allow_smaller_maxphyaddr:-)
next prev parent reply other threads:[~2021-10-21 17:13 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-19 11:01 [PATCH 0/4] KVM: X86: Improve guest TLB flushing Lai Jiangshan
2021-10-19 11:01 ` [PATCH 1/4] KVM: X86: Fix tlb flush for tdp in kvm_invalidate_pcid() Lai Jiangshan
2021-10-19 15:25 ` Sean Christopherson
2021-10-20 9:54 ` Lai Jiangshan
2021-10-20 18:26 ` Sean Christopherson
2021-10-21 1:27 ` Lai Jiangshan
2021-10-21 14:52 ` Sean Christopherson
2021-10-21 17:13 ` Paolo Bonzini [this message]
2021-10-21 17:32 ` Jim Mattson
2021-10-22 0:22 ` Lai Jiangshan
2021-10-19 11:01 ` [PATCH 2/4] KVM: X86: Cache CR3 in prev_roots when PCID is disabled Lai Jiangshan
2021-10-21 17:43 ` Paolo Bonzini
2021-10-22 2:11 ` Lai Jiangshan
2021-10-19 11:01 ` [PATCH 3/4] KVM: X86: Use smp_rmb() to pair with smp_wmb() in mmu_try_to_unsync_pages() Lai Jiangshan
2021-10-21 2:32 ` Lai Jiangshan
2021-10-21 17:44 ` Paolo Bonzini
2021-10-19 11:01 ` [PATCH 4/4] KVM: X86: Don't unload MMU in kvm_vcpu_flush_tlb_guest() Lai Jiangshan
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