Messages in this thread | | | Date | Mon, 07 Dec 2020 15:55:56 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH v6 1/2] arm64: kvm: Save/restore MTE registers |
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On 2020-12-07 14:48, Steven Price wrote: > On 03/12/2020 17:07, Marc Zyngier wrote: >> >>> diff --git a/arch/arm64/include/asm/sysreg.h >>> b/arch/arm64/include/asm/sysreg.h >>> index e2ef4c2edf06..b6668ffa04d9 100644 >>> --- a/arch/arm64/include/asm/sysreg.h >>> +++ b/arch/arm64/include/asm/sysreg.h >>> @@ -569,7 +569,8 @@ >>> #define SCTLR_ELx_M (BIT(0)) >>> >>> #define SCTLR_ELx_FLAGS (SCTLR_ELx_M | SCTLR_ELx_A | SCTLR_ELx_C >>> | \ >>> - SCTLR_ELx_SA | SCTLR_ELx_I | SCTLR_ELx_IESB) >>> + SCTLR_ELx_SA | SCTLR_ELx_I | SCTLR_ELx_IESB | \ >>> + SCTLR_ELx_ITFSB) >>> >>> /* SCTLR_EL2 specific flags. */ >>> #define SCTLR_EL2_RES1 ((BIT(4)) | (BIT(5)) | (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 cce43bfe158f..45255ba60152 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 @@ >>> static inline void __sysreg_save_common_state(struct kvm_cpu_context >>> *ctxt) >>> { >>> ctxt_sys_reg(ctxt, MDSCR_EL1) = read_sysreg(mdscr_el1); >>> + if (system_supports_mte()) { >> >> Please move the per-VM predicate to this patch so that it can be used >> not to save/restore the MTE registers if we don't need to. > > There isn't a valid struct kvm_vcpu or struct kvm here. I know there's > ctx->__hyp_running_vcpu but AFAICT that is only valid with the host > context.
We have per-CPU variables for the host context. If ctx->__hyp_running_vcpu is non NULL, you know you're on the host.
> >> >>> + ctxt_sys_reg(ctxt, RGSR_EL1) = >>> read_sysreg_s(SYS_RGSR_EL1); >>> + ctxt_sys_reg(ctxt, GCR_EL1) = read_sysreg_s(SYS_GCR_EL1); >>> + ctxt_sys_reg(ctxt, TFSRE0_EL1) = >>> read_sysreg_s(SYS_TFSRE0_EL1); >>> + } >> >> Overall, I still don't understand how this is going to work once >> we have MTE in the kernel. You mentioned having the ability to >> create turn off the tag checks at times, but I don't see that >> in this patch (and I'm not sure we want that either). > > Given that this is now highly unlikely to be merged for v5.11, I'll > rebase onto of the KASAN MTE series and double check exactly what > happens. My thought was that it should be as simple as setting TCO, > but your previous comment about moving the save/restore into assembler > might be wise in case the compiler starts playing with TCO itself.
Indeed.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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