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Tue, 25 Aug 2020 14:53:48 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 25 Aug 2020 14:53:47 +0100 From: Marc Zyngier To: Catalin Marinas Cc: Vincenzo Frascino , linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Will Deacon , Dave P Martin , Szabolcs Nagy , Kevin Brodsky , Andrey Konovalov , Peter Collingbourne , Andrew Morton , Suzuki K Poulose Subject: Re: [PATCH v8 03/28] arm64: mte: CPU feature detection and initial sysreg configuration In-Reply-To: <20200825105450.GA22233@C02TF0J2HF1T.local> References: <20200824182758.27267-1-catalin.marinas@arm.com> <20200824182758.27267-4-catalin.marinas@arm.com> <61bba3c1948651a5221b87f2dfa2872f@kernel.org> <20200825105450.GA22233@C02TF0J2HF1T.local> User-Agent: Roundcube Webmail/1.4.8 Message-ID: <8ef4b3d5d860346e47f4238bdb0f2a91@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: catalin.marinas@arm.com, vincenzo.frascino@arm.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, will@kernel.org, Dave.Martin@arm.com, szabolcs.nagy@arm.com, kevin.brodsky@arm.com, andreyknvl@google.com, pcc@google.com, akpm@linux-foundation.org, Suzuki.Poulose@arm.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: 5567728A4EC X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 2020-08-25 11:54, Catalin Marinas wrote: > On Tue, Aug 25, 2020 at 09:53:16AM +0100, Marc Zyngier wrote: >> On 2020-08-24 19:27, Catalin Marinas wrote: >> > diff --git a/arch/arm64/include/asm/kvm_arm.h >> > b/arch/arm64/include/asm/kvm_arm.h >> > index 8a1cbfd544d6..6c3b2fc922bb 100644 >> > --- a/arch/arm64/include/asm/kvm_arm.h >> > +++ b/arch/arm64/include/asm/kvm_arm.h >> > @@ -78,7 +78,7 @@ >> > HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW | HCR_TLOR | \ >> > HCR_FMO | HCR_IMO) >> > #define HCR_VIRT_EXCP_MASK (HCR_VSE | HCR_VI | HCR_VF) >> > -#define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK) >> > +#define HCR_HOST_NVHE_FLAGS (HCR_RW | HCR_API | HCR_APK | HCR_ATA) >> > #define HCR_HOST_VHE_FLAGS (HCR_RW | HCR_TGE | HCR_E2H) >> >> Why is HCR_ATA only set for nVHE? HCR_EL2.ATA seems to apply to both, >> doesn't it? > > We need HCR_EL2.ATA to be set when !VHE so that the host kernel can use > MTE. That said, I think we need to turn it off when running a guest. > Even if we hide the ID register, the guest may still attempt to enable > tags on some memory that doesn't support it, leading to unpredictable > behaviour (well, only if we expose device memory to guests directly; > Steve's patches will deal with this but for now we just disable MTE in > guests). > > With VHE, HCR_EL2.ATA only affects the guests, so it can stay off. The > host's use of tags is controlled by SCTLR_EL1/EL2.ATA (i.e. HCR_EL2.ATA > has no effect if E2H and TGE are both 1; qemu has a bug here which I > discovered yesterday). Ah, I missed that too. > >> > diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c >> > index 077293b5115f..59b91f58efec 100644 >> > --- a/arch/arm64/kvm/sys_regs.c >> > +++ b/arch/arm64/kvm/sys_regs.c >> > @@ -1131,6 +1131,8 @@ static u64 read_id_reg(const struct kvm_vcpu >> > *vcpu, >> > if (!vcpu_has_sve(vcpu)) >> > val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT); >> > val &= ~(0xfUL << ID_AA64PFR0_AMU_SHIFT); >> > + } else if (id == SYS_ID_AA64PFR1_EL1) { >> > + val &= ~(0xfUL << ID_AA64PFR1_MTE_SHIFT); >> >> Hiding the capability is fine, but where is the handling of trapping >> instructions done? They should result in an UNDEF being injected. > > They are a few new MTE-specific MSR/MRS which are trapped at EL2 but > since KVM doesn't understand them yet, shouldn't it already inject > undef back at EL1? That would be safer regardless of MTE support. An UNDEF will be injected, but not without spitting a nastygram in the kernel log (look at emulate_sys_reg()). The best course of action is to have an entry in the sysreg table that would explicitly do the handling. Thanks, M. -- Jazz is not dead. It just smells funny...