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From: Sean Christopherson <seanjc@google.com>
To: Mingwei Zhang <mizhang@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Ben Gardon <bgardon@google.com>,
	Jing Zhang <jingzhangos@google.com>
Subject: Re: [PATCH v2 2/3] KVM: x86/mmu: Avoid collision with !PRESENT SPTEs in TDP MMU lpage stats
Date: Thu, 29 Jul 2021 18:34:50 +0000	[thread overview]
Message-ID: <YQL0yjwYzJKJ0pTe@google.com> (raw)
In-Reply-To: <20210726175357.1572951-3-mizhang@google.com>

On Mon, Jul 26, 2021, Mingwei Zhang wrote:
> Factor in whether or not the old/new SPTEs are shadow-present when
> adjusting the large page stats in the TDP MMU. A modified MMIO SPTE can
> toggle the page size bit, as bit 7 is used to store the MMIO generation,
> i.e. is_large_pte() can get a false positive when called on a MMIO SPTE.
> Ditto for nuking SPTEs with REMOVED_SPTE, which sets bit 7 in its magic
> value.
> 
> Opportunistically move the logic below the check to verify at least one
> of the old/new SPTEs is shadow present.
> 
> Use is/was_leaf even though is/was_present would suffice.  The code
> generation is roughly equivalent since all flags need to be computed
> prior to the code in question, and using the *_leaf flags will minimize
> the diff in a future enhancement to account all pages, i.e. will change
> the check to "is_leaf != was_leaf".
> 
> Suggested-by: Sean Christopherson <seanjc@google.com>

There's no hard rule for when to use Suggested-by vs. giving Author credit, but
in this case, since you took the patch and changelog verbatim[*] (sans the missing
tags below), it's more polite to take the full patch (with me as Author in
this case) and add your SOB since you're posting the patch.

  Fixes: 1699f65c8b65 ("kvm/x86: Fix 'lpages' kvm stat for TDM MMU")
  Cc: stable@vger.kernel.org

[*] https://lkml.kernel.org/r/YPho0ME5pSjqRSoc@google.com

> Signed-off-by: Mingwei Zhang <mizhang@google.com>

  parent reply	other threads:[~2021-07-29 18:34 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 17:53 [PATCH v2 0/3] Add detailed page size stats in KVM stats Mingwei Zhang
2021-07-26 17:53 ` [PATCH v2 1/3] KVM: x86/mmu: Remove redundant spte present check in mmu_set_spte Mingwei Zhang
2021-07-26 20:23   ` Ben Gardon
2021-07-29 18:16   ` Sean Christopherson
2021-07-26 17:53 ` [PATCH v2 2/3] KVM: x86/mmu: Avoid collision with !PRESENT SPTEs in TDP MMU lpage stats Mingwei Zhang
2021-07-26 21:02   ` Ben Gardon
2021-07-29 18:34   ` Sean Christopherson [this message]
2021-07-29 19:01     ` Mingwei Zhang
2021-07-26 17:53 ` [PATCH v2 3/3] KVM: x86/mmu: Add detailed page size stats Mingwei Zhang
2021-07-26 20:41   ` Ben Gardon
2021-07-26 21:06     ` Ben Gardon
2021-07-29 18:45     ` Sean Christopherson
2021-07-29 19:02       ` Mingwei Zhang
2021-07-27 15:36   ` David Matlack
2021-07-29  6:24     ` Mingwei Zhang

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