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From: Sean Christopherson <seanjc@google.com>
To: Ben Gardon <bgardon@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,
	Hou Wenlong <houwenlong93@linux.alibaba.com>
Subject: Re: [PATCH 21/28] KVM: x86/mmu: Add TDP MMU helper to zap a root
Date: Mon, 22 Nov 2021 23:15:49 +0000	[thread overview]
Message-ID: <YZwkpcmAi07fOgbz@google.com> (raw)
In-Reply-To: <CANgfPd83-1yT=p1bMTRiOqCBq_m5AZuuhzmmyKKau9ODML39oA@mail.gmail.com>

On Mon, Nov 22, 2021, Ben Gardon wrote:
> On Fri, Nov 19, 2021 at 8:51 PM Sean Christopherson <seanjc@google.com> wrote:
> >
> > Add a small wrapper to handle zapping a specific root.  For now, it's
> > little more than syntactic sugar, but in the future it will become a
> > unique flow with rules specific to zapping an unreachable root.
> >
> > No functional change intended.
> >
> > Signed-off-by: Sean Christopherson <seanjc@google.com>
> > ---
> >  arch/x86/kvm/mmu/tdp_mmu.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index 9449cb5baf0b..31fb622249e5 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -79,11 +79,18 @@ static void tdp_mmu_free_sp_rcu_callback(struct rcu_head *head)
> >         tdp_mmu_free_sp(sp);
> >  }
> >
> > +static bool tdp_mmu_zap_root(struct kvm *kvm, struct kvm_mmu_page *root,
> > +                            bool shared)
> > +{
> > +       return zap_gfn_range(kvm, root, 0, -1ull, true, false, shared);
> 
> Total aside:
> Remembering the order of these three boolean parameters through all
> these functions drives me nuts.
> It'd be really nice to put them into a neat, reusable struct that tracks:
> MMU lock mode (read / write / none)
> If yielding is okay
> If the TLBs are dirty and need to be flushed
> 
> I don't know when I'll have time to do that refactor, but it would
> make this code so much more sensible.

Heh, I did exactly that, then threw away the code when I realized that I could
break up zap_gfn_range() into three separate helpers and avoid control knob hell
(spoiler alert for later patches in this series).

There are still two booleans (to what ends up being tdp_mmu_zap_leafs()), but none
none of the call sites pass true/false for _both_ params, so the call sites end up
being quite readable.  At that point, using a struct ended up being a net negative,
e.g. kvm_tdp_mmu_unmap_gfn_range() had to marshall from one struct to another.

  reply	other threads:[~2021-11-22 23:15 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-20  4:50 [PATCH 00/28] KVM: x86/mmu: Overhaul TDP MMU zapping and flushing Sean Christopherson
2021-11-20  4:50 ` [PATCH 01/28] KVM: x86/mmu: Use yield-safe TDP MMU root iter in MMU notifier unmapping Sean Christopherson
2021-11-22 19:48   ` Ben Gardon
2021-11-30  8:03   ` Paolo Bonzini
2021-11-20  4:50 ` [PATCH 02/28] KVM: x86/mmu: Skip tlb flush if it has been done in zap_gfn_range() Sean Christopherson
2021-11-20  4:50 ` [PATCH 03/28] KVM: x86/mmu: Remove spurious TLB flushes in TDP MMU zap collapsible path Sean Christopherson
2021-11-20  4:50 ` [PATCH 04/28] KVM: x86/mmu: Retry page fault if root is invalidated by memslot update Sean Christopherson
2021-11-22 19:54   ` Ben Gardon
2021-12-01 20:49   ` Paolo Bonzini
2021-12-08 19:17   ` Sean Christopherson
2021-11-20  4:50 ` [PATCH 05/28] KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP MMU Sean Christopherson
2021-11-22 19:57   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 06/28] KVM: x86/mmu: Formalize TDP MMU's (unintended?) deferred TLB flush logic Sean Christopherson
2021-11-20  4:50 ` [PATCH 07/28] KVM: x86/mmu: Document that zapping invalidated roots doesn't need to flush Sean Christopherson
2021-11-20  4:50 ` [PATCH 08/28] KVM: x86/mmu: Drop unused @kvm param from kvm_tdp_mmu_get_root() Sean Christopherson
2021-11-22 20:02   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 09/28] KVM: x86/mmu: Require mmu_lock be held for write in unyielding root iter Sean Christopherson
2021-11-22 20:10   ` Ben Gardon
2021-11-22 20:19     ` Sean Christopherson
2021-11-20  4:50 ` [PATCH 10/28] KVM: x86/mmu: Allow yielding when zapping GFNs for defunct TDP MMU root Sean Christopherson
2021-11-22 21:30   ` Ben Gardon
2021-11-22 22:40     ` Sean Christopherson
2021-11-22 23:03       ` Ben Gardon
2021-12-14 23:45     ` Sean Christopherson
2021-12-14 23:52       ` Sean Christopherson
2021-11-20  4:50 ` [PATCH 11/28] KVM: x86/mmu: Check for !leaf=>leaf, not PFN change, in TDP MMU SP removal Sean Christopherson
2021-11-20  4:50 ` [PATCH 12/28] KVM: x86/mmu: Batch TLB flushes from TDP MMU for MMU notifier change_spte Sean Christopherson
2021-11-22 21:45   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 13/28] KVM: x86/mmu: Drop RCU after processing each root in MMU notifier hooks Sean Christopherson
2021-11-22 21:47   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 14/28] KVM: x86/mmu: Add helpers to read/write TDP MMU SPTEs and document RCU Sean Christopherson
2021-11-22 21:55   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 15/28] KVM: x86/mmu: Take TDP MMU roots off list when invalidating all roots Sean Christopherson
2021-11-22 22:20   ` Ben Gardon
2021-11-22 23:08     ` Sean Christopherson
2021-11-23  0:03       ` Ben Gardon
2021-12-14 23:34         ` Sean Christopherson
2021-11-20  4:50 ` [PATCH 16/28] KVM: x86/mmu: WARN if old _or_ new SPTE is REMOVED in non-atomic path Sean Christopherson
2021-11-22 21:57   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 17/28] KVM: x86/mmu: Terminate yield-friendly walk if invalid root observed Sean Christopherson
2021-11-22 22:25   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 18/28] KVM: x86/mmu: Refactor low-level TDP MMU set SPTE helper to take raw vals Sean Christopherson
2021-11-22 22:29   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 19/28] KVM: x86/mmu: Zap only the target TDP MMU shadow page in NX recovery Sean Christopherson
2021-11-22 22:43   ` Ben Gardon
2021-11-23  1:16     ` Sean Christopherson
2021-11-23 19:35       ` Ben Gardon
2021-11-20  4:50 ` [PATCH 20/28] KVM: x86/mmu: Use common TDP MMU zap helper for MMU notifier unmap hook Sean Christopherson
2021-11-22 22:49   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 21/28] KVM: x86/mmu: Add TDP MMU helper to zap a root Sean Christopherson
2021-11-22 22:54   ` Ben Gardon
2021-11-22 23:15     ` Sean Christopherson [this message]
2021-11-22 23:38       ` Ben Gardon
2021-11-20  4:50 ` [PATCH 22/28] KVM: x86/mmu: Skip remote TLB flush when zapping all of TDP MMU Sean Christopherson
2021-11-22 23:00   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 23/28] KVM: x86/mmu: Use "zap root" path for "slow" zap of all TDP MMU SPTEs Sean Christopherson
2021-11-20  4:50 ` [PATCH 24/28] KVM: x86/mmu: Add dedicated helper to zap TDP MMU root shadow page Sean Christopherson
2021-11-23  1:04   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 25/28] KVM: x86/mmu: Require mmu_lock be held for write to zap TDP MMU range Sean Christopherson
2021-11-23 19:58   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 26/28] KVM: x86/mmu: Zap only TDP MMU leafs in kvm_zap_gfn_range() Sean Christopherson
2021-11-23 19:58   ` Ben Gardon
2021-11-20  4:50 ` [PATCH 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched Sean Christopherson
2021-11-23 19:58   ` Ben Gardon
2021-11-24 18:42     ` Sean Christopherson
2021-11-30 11:29   ` Paolo Bonzini
2021-11-30 15:45     ` Sean Christopherson
2021-11-30 16:16       ` Paolo Bonzini
2021-11-20  4:50 ` [PATCH 28/28] KVM: x86/mmu: Defer TLB flush to caller when freeing TDP MMU shadow pages Sean Christopherson
2021-11-23 20:12   ` Ben Gardon
2021-12-01 17:53 ` [PATCH 00/28] KVM: x86/mmu: Overhaul TDP MMU zapping and flushing David Matlack
2021-12-02  2:03   ` Sean Christopherson
2021-12-03  0:16     ` David Matlack

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