From mboxrd@z Thu Jan  1 00:00:00 1970
From: Steven Price <steven.price@arm.com>
Subject: Re: [PATCH v6 02/26] arm64: mte: CPU feature detection and initial
 sysreg configuration
Date: Mon, 13 Jul 2020 11:08:15 +0100
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References: <20200703153718.16973-1-catalin.marinas@arm.com>
 <20200703153718.16973-3-catalin.marinas@arm.com>
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To: Catalin Marinas <catalin.marinas@arm.com>, linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org, Suzuki K Poulose <Suzuki.Poulose@arm.com>, Szabolcs Nagy <szabolcs.nagy@arm.com>, Andrey Konovalov <andreyknvl@google.com>, Kevin Brodsky <kevin.brodsky@arm.com>, Peter Collingbourne <pcc@google.com>, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Will Deacon <will@kernel.org>, Dave P Martin <Dave.Martin@arm.com>

On 03/07/2020 16:36, Catalin Marinas wrote:
> From: Vincenzo Frascino <vincenzo.frascino@arm.com>
> 
> Add the cpufeature and hwcap entries to detect the presence of MTE on
> the boot CPUs (primary and secondary). Any late secondary CPU not
> supporting the feature, if detected during boot, will be parked.
> 
> In addition, add the minimum SCTLR_EL1 and HCR_EL2 bits for enabling
> MTE. Without subsequent setting of MAIR, these bits do not have an
> effect on tag checking.
> 
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Co-developed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Suzuki K Poulose <Suzuki.Poulose@arm.com>

This commit causes the feature bit to be exposed to a guest, but we
don't at this point have any way of handling a guest which attempts to
use MTE.

This is 'fixed' by the first patch of my KVM MTE series[1], but perhaps
the chunk modifying arch/arm64/kvm/sys_regs.c (see below) should be included here
instead? That way we hide the feature until we're ready for a guest with
MTE support.

Steve
  [1] https://lore.kernel.org/r/20200713100102.53664-2-steven.price@arm.com

----8<----
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index baf5ce9225ce..5ca974c93bd4 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1104,6 +1104,8 @@ 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);
  	} else if (id == SYS_ID_AA64ISAR1_EL1 && !vcpu_has_ptrauth(vcpu)) {
  		val &= ~((0xfUL << ID_AA64ISAR1_APA_SHIFT) |
  			 (0xfUL << ID_AA64ISAR1_API_SHIFT) |