From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Upton Date: Fri, 31 May 2024 12:18:11 -0700 Subject: [PATCH v4 6/7] KVM: arm64: Relax locking for kvm_test_age_gfn and kvm_age_gfn In-Reply-To: References: <20240529180510.2295118-1-jthoughton@google.com> <20240529180510.2295118-7-jthoughton@google.com> Message-ID: List-Id: To: kvm-riscv@lists.infradead.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Fri, May 31, 2024 at 12:11:33PM -0700, Oliver Upton wrote: > On Wed, May 29, 2024 at 06:05:09PM +0000, James Houghton wrote: > > [...] > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index 9e2bbee77491..eabb07c66a07 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -1319,10 +1319,8 @@ static int stage2_age_walker(const struct kvm_pgtable_visit_ctx *ctx, > > data->young = true; > > > > /* > > - * stage2_age_walker() is always called while holding the MMU lock for > > - * write, so this will always succeed. Nonetheless, this deliberately > > - * follows the race detection pattern of the other stage-2 walkers in > > - * case the locking mechanics of the MMU notifiers is ever changed. > > + * This walk may not be exclusive; the PTE is permitted to change > > + * from under us. > > */ > > if (data->mkold && !stage2_try_set_pte(ctx, new)) > > return -EAGAIN; > > It is probably worth mentioning that if there was a race to update the > PTE then the GFN is most likely young, so failing to clear AF probably > isn't even consequential. Oh, and the WARN_ON() in kvm_pgtable_stage2_test_clear_young() is bogus now. Maybe demote it to: r = kvm_pgtable_walk(...); WARN_ON_ONCE(r && r != -EAGAIN); -- Thanks, Oliver