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Sat, 25 Jul 2020 18:40:13 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Sat, 25 Jul 2020 18:40:13 +0100 From: Marc Zyngier To: Zhenyu Ye Cc: james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, steven.price@arm.com, mark.rutland@arm.com, ascull@google.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, arm@kernel.org, xiexiangyou@huawei.com Subject: Re: [RESEND RFC PATCH v1] arm64: kvm: flush tlbs by range in unmap_stage2_range function In-Reply-To: <20200724134315.805-1-yezhenyu2@huawei.com> References: <20200724134315.805-1-yezhenyu2@huawei.com> User-Agent: Roundcube Webmail/1.4.5 Message-ID: <5d54c860b3b4e7a98e4d53397e6424ae@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: yezhenyu2@huawei.com, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, steven.price@arm.com, mark.rutland@arm.com, ascull@google.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, arm@kernel.org, xiexiangyou@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-Rspamd-Queue-Id: C65FD3D674 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2020-07-24 14:43, Zhenyu Ye wrote: > Now in unmap_stage2_range(), we flush tlbs one by one just after the > corresponding pages cleared. However, this may cause some performance > problems when the unmap range is very large (such as when the vm > migration rollback, this may cause vm downtime too loog). You keep resending this patch, but you don't give any numbers that would back your assertion. > This patch moves the kvm_tlb_flush_vmid_ipa() out of loop, and > flush tlbs by range after other operations completed. Because we > do not make new mapping for the pages here, so this doesn't violate > the Break-Before-Make rules. > > Signed-off-by: Zhenyu Ye > --- > arch/arm64/include/asm/kvm_asm.h | 2 ++ > arch/arm64/kvm/hyp/tlb.c | 36 ++++++++++++++++++++++++++++++++ > arch/arm64/kvm/mmu.c | 11 +++++++--- > 3 files changed, 46 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_asm.h > b/arch/arm64/include/asm/kvm_asm.h > index 352aaebf4198..ef8203d3ca45 100644 > --- a/arch/arm64/include/asm/kvm_asm.h > +++ b/arch/arm64/include/asm/kvm_asm.h > @@ -61,6 +61,8 @@ extern char __kvm_hyp_vector[]; > > extern void __kvm_flush_vm_context(void); > extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t > ipa); > +extern void __kvm_tlb_flush_vmid_range(struct kvm *kvm, phys_addr_t > start, > + phys_addr_t end); > extern void __kvm_tlb_flush_vmid(struct kvm *kvm); > extern void __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu); > > diff --git a/arch/arm64/kvm/hyp/tlb.c b/arch/arm64/kvm/hyp/tlb.c > index d063a576d511..4f4737a7e588 100644 > --- a/arch/arm64/kvm/hyp/tlb.c > +++ b/arch/arm64/kvm/hyp/tlb.c > @@ -189,6 +189,42 @@ void __hyp_text __kvm_tlb_flush_vmid_ipa(struct > kvm *kvm, phys_addr_t ipa) > __tlb_switch_to_host(kvm, &cxt); > } > > +void __hyp_text __kvm_tlb_flush_vmid_range(struct kvm *kvm, > phys_addr_t start, > + phys_addr_t end) > +{ > + struct tlb_inv_context cxt; > + unsigned long addr; > + > + start = __TLBI_VADDR(start, 0); > + end = __TLBI_VADDR(end, 0); > + > + dsb(ishst); > + > + /* Switch to requested VMID */ > + kvm = kern_hyp_va(kvm); > + __tlb_switch_to_guest(kvm, &cxt); > + > + if ((end - start) >= 512 << (PAGE_SHIFT - 12)) { > + __tlbi(vmalls12e1is); And what is this magic value based on? You don't even mention in the commit log that you are taking this shortcut. > + goto end; > + } > + > + for (addr = start; addr < end; addr += 1 << (PAGE_SHIFT - 12)) > + __tlbi(ipas2e1is, addr); > + > + dsb(ish); > + __tlbi(vmalle1is); > + > +end: > + dsb(ish); > + isb(); > + > + if (!has_vhe() && icache_is_vpipt()) > + __flush_icache_all(); > + > + __tlb_switch_to_host(kvm, &cxt); > +} > + I'm sorry, but without numbers backing this approach for a number of workloads and a representative set of platforms, this is going nowhere. Thanks, M. -- Jazz is not dead. It just smells funny...