From: Suzuki K Poulose <suzuki.poulose@arm.com>
Date: Tue, 23 Mar 2021 12:06:29 +0000
Subject: KVM: arm64: Hide system instruction access to Trace registers
Git-commit: 1d676673d665fd2162e7e466dcfbe5373bfdb73e
Patch-mainline: v5.12-rc6
References: git-fixes

Currently we advertise the ID_AA6DFR0_EL1.TRACEVER for the guest,
when the trace register accesses are trapped (CPTR_EL2.TTA == 1).
So, the guest will get an undefined instruction, if trusts the
ID registers and access one of the trace registers.
Lets be nice to the guest and hide the feature to avoid
unexpected behavior.

Even though this can be done at KVM sysreg emulation layer,
we do this by removing the TRACEVER from the sanitised feature
register field. This is fine as long as the ETM drivers
can handle the individual trace units separately, even
when there are differences among the CPUs.

Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210323120647.454211-2-suzuki.poulose@arm.com

Acked-by: Ivan T. Ivanov <iivanov@suse.de>
---
 arch/arm64/kernel/cpufeature.c |    1 -
 1 file changed, 1 deletion(-)

--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -252,7 +252,6 @@ static const struct arm64_ftr_bits ftr_i
 	 * of support.
 	 */
 	S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_NONSTRICT, FTR_EXACT, ID_AA64DFR0_PMUVER_SHIFT, 4, 0),
-	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64DFR0_TRACEVER_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_EXACT, ID_AA64DFR0_DEBUGVER_SHIFT, 4, 0x6),
 	ARM64_FTR_END,
 };