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Mon, 08 Mar 2021 16:49:17 +0000 Received: from mail.kernel.org ([198.145.29.99]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lJJ49-001AND-NJ for linux-arm-kernel@lists.infradead.org; Mon, 08 Mar 2021 16:49:12 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 211856518D; Mon, 8 Mar 2021 16:49:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1615222147; bh=DVQbndAkIml65LX9jhn2q+DfBf8VuoyQTUefFkaqPEo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=tWgWGGXkCUyhjf/GVVWLdQ6LjYCbv/H7gIus4CH46j4UVAMEKovo6/HoMTLjD91OO kjC2nPfUn8FtupBItp4dFse1GKcy5H0OVhZ2DONYWx6ZTgAfopZRbualOyhX46bZYM vlnsM8EMVi4xKMtwSN9SvQVfsg7F2w/MfMmGPH16y+QEfBTyErncsNG+S1Eo+BZzCL MVuRvnDWvxpcd7bZd778QrI/cBsxAJwBTzihcY96SrG9WFe6tVKalO6n4yJGlWdOxA 4DQhY0DgZkMb0e8rhjeO+OUV0Uxg/grRb49P+8OX/lXVrLk87VYEsBxbfZ4i0EM3aA k3rWoqY3Stj5g== Date: Mon, 8 Mar 2021 16:49:02 +0000 From: Will Deacon To: Jing Zhang Cc: maz@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, qperret@google.com Subject: Re: [PATCH] KVM: arm64: Remove redundant check for S2FWB Message-ID: <20210308164902.GA26772@willie-the-truck> References: <20210205044403.1559010-1-jingzhangos@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210205044403.1559010-1-jingzhangos@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210308_164910_322544_BF27F95C X-CRM114-Status: GOOD ( 23.47 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Feb 05, 2021 at 04:44:03AM +0000, Jing Zhang wrote: > Remove redundant check for CPU feature S2FWB in dcache flush code > to save some CPU cycles for every memslot flush and unmapping. > And move the S2FWB check to outer functions to avoid future > redundancy and keep consistent with other usage like in > access_dcsw and kvm_arch_prepare_memory_region. > > Signed-off-by: Jing Zhang > --- > arch/arm64/kvm/hyp/pgtable.c | 9 ++------- > arch/arm64/kvm/mmu.c | 3 ++- > 2 files changed, 4 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index bdf8e55ed308..afd57564b1cb 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -642,9 +642,6 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size, > > static void stage2_flush_dcache(void *addr, u64 size) > { > - if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) > - return; > - > __flush_dcache_area(addr, size); > } > > @@ -670,7 +667,8 @@ static int stage2_unmap_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep, > > if (page_count(virt_to_page(childp)) != 1) > return 0; > - } else if (stage2_pte_cacheable(pte)) { > + } else if (stage2_pte_cacheable(pte) && > + !cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) { > need_flush = true; > } > > @@ -846,9 +844,6 @@ int kvm_pgtable_stage2_flush(struct kvm_pgtable *pgt, u64 addr, u64 size) > .flags = KVM_PGTABLE_WALK_LEAF, > }; > > - if (cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) > - return 0; > - > return kvm_pgtable_walk(pgt, addr, size, &walker); > } I think we should leave pgtable.c as it is: there's no benefit from this change on the unmap path, and the other path involves the case where the caller has asked for a flush and we can elide it. > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 7d2257cc5438..53130ed23304 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1458,7 +1458,8 @@ void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled) > * If switching it off, need to clean the caches. > * Clean + invalidate does the trick always. > */ > - if (now_enabled != was_enabled) > + if (now_enabled != was_enabled && > + !cpus_have_const_cap(ARM64_HAS_STAGE2_FWB)) > stage2_flush_vm(vcpu->kvm); This change looks fine, but I don't grok the justification in your follow-up email. You say: | The saving is from the code path of memslot flush. The S2FWB check was | in stage2_flush_dcache, in which case, for a memslot flush, the check | was done for every page. but I don't see where this is called for every page. It looks to me like it's called for every pgd in the range, which is a very different kettle of frogs. What am I missing? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel