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Wed, 18 Nov 2020 17:02:44 +0000 (UTC) Date: Wed, 18 Nov 2020 17:02:41 +0000 From: Catalin Marinas To: Steven Price Subject: Re: [PATCH v4 1/2] arm64: kvm: Save/restore MTE registers Message-ID: References: <20201026155727.36685-1-steven.price@arm.com> <20201026155727.36685-2-steven.price@arm.com> <98eaa539-0ae8-ce4c-8886-3040542ede80@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <98eaa539-0ae8-ce4c-8886-3040542ede80@arm.com> Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Marc Zyngier , Juan Quintela , Richard Henderson , linux-kernel@vger.kernel.org, Dave Martin , linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Will Deacon , kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Wed, Nov 18, 2020 at 04:01:18PM +0000, Steven Price wrote: > On 17/11/2020 19:20, Marc Zyngier wrote: > > On 2020-10-26 15:57, Steven Price wrote: > > > diff --git a/arch/arm64/include/asm/sysreg.h > > > b/arch/arm64/include/asm/sysreg.h > > > index d52c1b3ce589..7727df0bc09d 100644 > > > --- a/arch/arm64/include/asm/sysreg.h > > > +++ b/arch/arm64/include/asm/sysreg.h > > > @@ -565,7 +565,8 @@ > > > =A0#define SCTLR_ELx_M=A0=A0=A0 (BIT(0)) > > > = > > > =A0#define SCTLR_ELx_FLAGS=A0=A0=A0 (SCTLR_ELx_M=A0 | SCTLR_ELx_A | S= CTLR_ELx_C | \ > > > -=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 SCTLR_ELx_SA | SCTLR_ELx_I | SC= TLR_ELx_IESB) > > > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 SCTLR_ELx_SA | SCTLR_ELx_I | SC= TLR_ELx_IESB | \ > > > +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 SCTLR_ELx_ITFSB) > > > = > > > =A0/* SCTLR_EL2 specific flags. */ > > > =A0#define SCTLR_EL2_RES1=A0=A0=A0 ((BIT(4))=A0 | (BIT(5))=A0 | (BIT(= 11)) | > > > (BIT(16)) | \ > > > diff --git a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h > > > b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h > > > index 7a986030145f..a124ffa49ba3 100644 > > > --- a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h > > > +++ b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h > > > @@ -18,6 +18,11 @@ > > > =A0static inline void __sysreg_save_common_state(struct > > > kvm_cpu_context *ctxt) > > > =A0{ > > > =A0=A0=A0=A0 ctxt_sys_reg(ctxt, MDSCR_EL1)=A0=A0=A0 =3D read_sysreg(m= dscr_el1); > > > +=A0=A0=A0 if (system_supports_mte()) { > > > +=A0=A0=A0=A0=A0=A0=A0 ctxt_sys_reg(ctxt, RGSR_EL1)=A0=A0=A0 =3D read= _sysreg_s(SYS_RGSR_EL1); > > > +=A0=A0=A0=A0=A0=A0=A0 ctxt_sys_reg(ctxt, GCR_EL1)=A0=A0=A0 =3D read_= sysreg_s(SYS_GCR_EL1); > > > +=A0=A0=A0=A0=A0=A0=A0 ctxt_sys_reg(ctxt, TFSRE0_EL1)=A0=A0=A0 =3D > > > read_sysreg_s(SYS_TFSRE0_EL1); > > = > > As far as I can tell, HCR_EL2.ATA is still clear when running a guest. > > So why, do we save/restore this state yet? > > = > > Also, I wonder whether we should keep these in the C code. If one day > > we enable MTE in the kernel, we will have to move them to the assembly > > part, much like we do for PAuth. And I fear that "one day" is pretty > > soon: > > = > > https://lore.kernel.org/linux-arm-kernel/cover.1605046192.git.andreyknv= l@google.com/ > = > Good point. Although for MTE we do have the option of setting TCO in PSTA= TE > so this could remain in C if we're not bothered about the 'gap' in KASAN > coverage. I haven't yet got my head around how (or indeed if) that series > handles guests. I think we should be fine with the currently proposed in-kernel MTE support. However, setting GCR_EL1 can get in the way if stack tagging is ever enabled (it breaks single image). The compiler uses GCR_EL1 to generate different colours for variables on the stack and changing it in the middle of a function may cause confusion. You'd have to set PSTATE.TCO for the whole function, either from the caller or, if the compiler gets smarter, some function attribute. -- = Catalin _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm