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Thu, 20 May 2021 08:51:42 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AC62D60241; Thu, 20 May 2021 08:51:37 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1ljeP1-002Sgn-GH; Thu, 20 May 2021 09:51:35 +0100 Date: Thu, 20 May 2021 09:51:28 +0100 Message-ID: <875yzdvldb.wl-maz@kernel.org> From: Marc Zyngier To: Steven Price Cc: Catalin Marinas , Will Deacon , James Morse , Julien Thierry , Suzuki K Poulose , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Martin , Mark Rutland , Thomas Gleixner , qemu-devel@nongnu.org, Juan Quintela , "Dr. David Alan Gilbert" , Richard Henderson , Peter Maydell , Haibo Xu , Andrew Jones Subject: Re: [PATCH v12 4/8] arm64: kvm: Introduce MTE VM feature In-Reply-To: <60fc8939-36b7-35ce-837c-b69d0d40c9a4@arm.com> References: <20210517123239.8025-1-steven.price@arm.com> <20210517123239.8025-5-steven.price@arm.com> <87wnrxtikl.wl-maz@kernel.org> <60fc8939-36b7-35ce-837c-b69d0d40c9a4@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: steven.price@arm.com, catalin.marinas@arm.com, will@kernel.org, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Dave.Martin@arm.com, mark.rutland@arm.com, tglx@linutronix.de, qemu-devel@nongnu.org, quintela@redhat.com, dgilbert@redhat.com, richard.henderson@linaro.org, peter.maydell@linaro.org, Haibo.Xu@arm.com, drjones@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210520_015140_191992_20F8E8F4 X-CRM114-Status: GOOD ( 66.94 ) 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 Wed, 19 May 2021 11:48:21 +0100, Steven Price wrote: > > On 17/05/2021 17:45, Marc Zyngier wrote: > > On Mon, 17 May 2021 13:32:35 +0100, > > Steven Price wrote: > >> > >> Add a new VM feature 'KVM_ARM_CAP_MTE' which enables memory tagging > >> for a VM. This will expose the feature to the guest and automatically > >> tag memory pages touched by the VM as PG_mte_tagged (and clear the tag > >> storage) to ensure that the guest cannot see stale tags, and so that > >> the tags are correctly saved/restored across swap. > >> > >> Actually exposing the new capability to user space happens in a later > >> patch. > > > > uber nit in $SUBJECT: "KVM: arm64:" is the preferred prefix (just like > > patches 7 and 8). > > Good spot - I obviously got carried away with the "arm64:" prefix ;) > > >> > >> Signed-off-by: Steven Price > >> --- > >> arch/arm64/include/asm/kvm_emulate.h | 3 +++ > >> arch/arm64/include/asm/kvm_host.h | 3 +++ > >> arch/arm64/kvm/hyp/exception.c | 3 ++- > >> arch/arm64/kvm/mmu.c | 37 +++++++++++++++++++++++++++- > >> arch/arm64/kvm/sys_regs.c | 3 +++ > >> include/uapi/linux/kvm.h | 1 + > >> 6 files changed, 48 insertions(+), 2 deletions(-) > >> > >> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h > >> index f612c090f2e4..6bf776c2399c 100644 > >> --- a/arch/arm64/include/asm/kvm_emulate.h > >> +++ b/arch/arm64/include/asm/kvm_emulate.h > >> @@ -84,6 +84,9 @@ static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu) > >> if (cpus_have_const_cap(ARM64_MISMATCHED_CACHE_TYPE) || > >> vcpu_el1_is_32bit(vcpu)) > >> vcpu->arch.hcr_el2 |= HCR_TID2; > >> + > >> + if (kvm_has_mte(vcpu->kvm)) > >> + vcpu->arch.hcr_el2 |= HCR_ATA; > >> } > >> > >> static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu) > >> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h > >> index 7cd7d5c8c4bc..afaa5333f0e4 100644 > >> --- a/arch/arm64/include/asm/kvm_host.h > >> +++ b/arch/arm64/include/asm/kvm_host.h > >> @@ -132,6 +132,8 @@ struct kvm_arch { > >> > >> u8 pfr0_csv2; > >> u8 pfr0_csv3; > >> + /* Memory Tagging Extension enabled for the guest */ > >> + bool mte_enabled; > >> }; > >> > >> struct kvm_vcpu_fault_info { > >> @@ -769,6 +771,7 @@ bool kvm_arm_vcpu_is_finalized(struct kvm_vcpu *vcpu); > >> #define kvm_arm_vcpu_sve_finalized(vcpu) \ > >> ((vcpu)->arch.flags & KVM_ARM64_VCPU_SVE_FINALIZED) > >> > >> +#define kvm_has_mte(kvm) (system_supports_mte() && (kvm)->arch.mte_enabled) > >> #define kvm_vcpu_has_pmu(vcpu) \ > >> (test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features)) > >> > >> diff --git a/arch/arm64/kvm/hyp/exception.c b/arch/arm64/kvm/hyp/exception.c > >> index 73629094f903..56426565600c 100644 > >> --- a/arch/arm64/kvm/hyp/exception.c > >> +++ b/arch/arm64/kvm/hyp/exception.c > >> @@ -112,7 +112,8 @@ static void enter_exception64(struct kvm_vcpu *vcpu, unsigned long target_mode, > >> new |= (old & PSR_C_BIT); > >> new |= (old & PSR_V_BIT); > >> > >> - // TODO: TCO (if/when ARMv8.5-MemTag is exposed to guests) > >> + if (kvm_has_mte(vcpu->kvm)) > >> + new |= PSR_TCO_BIT; > >> > >> new |= (old & PSR_DIT_BIT); > >> > >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > >> index c5d1f3c87dbd..8660f6a03f51 100644 > >> --- a/arch/arm64/kvm/mmu.c > >> +++ b/arch/arm64/kvm/mmu.c > >> @@ -822,6 +822,31 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot, > >> return PAGE_SIZE; > >> } > >> > >> +static int sanitise_mte_tags(struct kvm *kvm, unsigned long size, > >> + kvm_pfn_t pfn) > > > > Nit: please order the parameters as address, then size. > > Sure > > >> +{ > >> + if (kvm_has_mte(kvm)) { > >> + /* > >> + * The page will be mapped in stage 2 as Normal Cacheable, so > >> + * the VM will be able to see the page's tags and therefore > >> + * they must be initialised first. If PG_mte_tagged is set, > >> + * tags have already been initialised. > >> + */ > >> + unsigned long i, nr_pages = size >> PAGE_SHIFT; > >> + struct page *page = pfn_to_online_page(pfn); > >> + > >> + if (!page) > >> + return -EFAULT; > > > > Under which circumstances can this happen? We already have done a GUP > > on the page, so I really can't see how the page can vanish from under > > our feet. > > It's less about the page vanishing and more that pfn_to_online_page() > will reject some pages. Specifically in this case we want to reject any > sort of device memory (e.g. graphics card memory or other memory on the > end of a bus like PCIe) as it is unlikely to support MTE. OK. We really never should see this error as we check for device mappings right before calling this, but I guess it doesn't hurt. > > >> + > >> + for (i = 0; i < nr_pages; i++, page++) { > >> + if (!test_and_set_bit(PG_mte_tagged, &page->flags)) > >> + mte_clear_page_tags(page_address(page)); > > > > You seem to be doing this irrespective of the VMA being created with > > PROT_MTE. This is fine form a guest perspective (all its memory should > > be MTE capable). However, I can't see any guarantee that the VMM will > > actually allocate memslots with PROT_MTE. > > > > Aren't we missing some sanity checks at memslot registration time? > > I've taken the decision not to require that the VMM allocates with > PROT_MTE, there are two main reasons for this: > > 1. The VMM generally doesn't actually want a PROT_MTE mapping as the > tags from the guest are almost certainly wrong for most usages (e.g. > device emulation). So a PROT_MTE mapping actively gets in the way of the > VMM using MTE for it's own purposes. However this then leads to the > requirement for the new ioctl in patch 7. > > 2. Because the VMM can change the pages in a memslot at any time and > KVM relies on mmu notifiers to spot the change it's hard and ugly to > enforce that the memslot VMAs keep having the PROT_MTE flag. When I > tried this it meant we've discover that a page doesn't have the MTE flag > at fault time and have no other option that to kill the VM at that time. > > So the model is that non-PROT_MTE memory can be supplied to the memslots > and KVM will automatically upgrade it to PG_mte_tagged if you supply it > to a VM with MTE enabled. This makes the VMM implementation easier for > most cases, and the new ioctl helps for migration. I think the kernel > code is tidier too. OK, I see your point. I guess we rely on the implicit requirement that all the available memory is MTE-capable, although I'm willing to bet that someone will eventually break this requirement. > Of course even better would be a stage 2 flag to control MTE > availability on a page-by-page basis, but that doesn't exist in the > architecture at the moment. Nah, that'd be way too good. Let's not do that. > > >> + } > >> + } > >> + > >> + return 0; > >> +} > >> + > >> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >> struct kvm_memory_slot *memslot, unsigned long hva, > >> unsigned long fault_status) > >> @@ -971,8 +996,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > >> if (writable) > >> prot |= KVM_PGTABLE_PROT_W; > >> > >> - if (fault_status != FSC_PERM && !device) > >> + if (fault_status != FSC_PERM && !device) { > >> + ret = sanitise_mte_tags(kvm, vma_pagesize, pfn); > >> + if (ret) > >> + goto out_unlock; > >> + > >> clean_dcache_guest_page(pfn, vma_pagesize); > >> + } > >> > >> if (exec_fault) { > >> prot |= KVM_PGTABLE_PROT_X; > >> @@ -1168,12 +1198,17 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range) > >> bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range) > >> { > >> kvm_pfn_t pfn = pte_pfn(range->pte); > >> + int ret; > >> > >> if (!kvm->arch.mmu.pgt) > >> return 0; > >> > >> WARN_ON(range->end - range->start != 1); > >> > >> + ret = sanitise_mte_tags(kvm, PAGE_SIZE, pfn); > >> + if (ret) > >> + return ret; > > > > Notice the change in return type? > > I do now - I was tricked by the use of '0' as false. Looks like false > ('0') is actually the correct return here to avoid an unnecessary > kvm_flush_remote_tlbs(). Yup. BTW, the return values have been fixed to proper boolean types in the latest set of fixes. > > >> + > >> /* > >> * We've moved a page around, probably through CoW, so let's treat it > >> * just like a translation fault and clean the cache to the PoC. > >> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c > >> index 76ea2800c33e..24a844cb79ca 100644 > >> --- a/arch/arm64/kvm/sys_regs.c > >> +++ b/arch/arm64/kvm/sys_regs.c > >> @@ -1047,6 +1047,9 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, > >> break; > >> case SYS_ID_AA64PFR1_EL1: > >> val &= ~FEATURE(ID_AA64PFR1_MTE); > >> + if (kvm_has_mte(vcpu->kvm)) > >> + val |= FIELD_PREP(FEATURE(ID_AA64PFR1_MTE), > >> + ID_AA64PFR1_MTE); > > > > Shouldn't this be consistent with what the HW is capable of > > (i.e. FEAT_MTE3 if available), and extracted from the sanitised view > > of the feature set? > > Yes - however at the moment our sanitised view is either FEAT_MTE2 or > nothing: > > { > .desc = "Memory Tagging Extension", > .capability = ARM64_MTE, > .type = ARM64_CPUCAP_STRICT_BOOT_CPU_FEATURE, > .matches = has_cpuid_feature, > .sys_reg = SYS_ID_AA64PFR1_EL1, > .field_pos = ID_AA64PFR1_MTE_SHIFT, > .min_field_value = ID_AA64PFR1_MTE, > .sign = FTR_UNSIGNED, > .cpu_enable = cpu_enable_mte, > }, > > When host support for FEAT_MTE3 is added then the KVM code will need > revisiting to expose that down to the guest safely (AFAICS there's > nothing extra to do here, but I haven't tested any of the MTE3 > features). I don't think we want to expose newer versions to the guest > than the host is aware of. (Or indeed expose FEAT_MTE if the host has > MTE disabled because Linux requires at least FEAT_MTE2). What I was suggesting is to have something like this: pfr = read_sanitised_ftr_reg(SYS_ID_AA64PFR1_EL1); mte = cpuid_feature_extract_unsigned_field(pfr, ID_AA64PFR1_MTE_SHIFT); val |= FIELD_PREP(FEATURE(ID_AA64PFR1_MTE), mte); which does the trick nicely, and doesn't expose more than the host supports. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel