Re: [PATCH V4 15/17] arm64/cpufeature: Add remaining feature bits in ID_AA64DFR0 register

On 05/24/2020 02:08 AM, Anshuman Khandual wrote:

On 05/20/2020 07:27 PM, Suzuki K Poulose wrote:

quoted

On 05/19/2020 10:40 AM, Anshuman Khandual wrote:

quoted

Enable MTPMU and TRACEFILT features bits in ID_AA64DFR0 register as per ARM
DDI 0487F.a specification.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Anshuman Khandual <redacted>
---
   arch/arm64/include/asm/sysreg.h | 2 ++
   arch/arm64/kernel/cpufeature.c  | 2 ++
   2 files changed, 4 insertions(+)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index a572069ccf6e..4bcd21cc2d68 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h

@@ -766,6 +766,8 @@
   #define ID_AA64MMFR2_CNP_SHIFT        0
     /* id_aa64dfr0 */
+#define ID_AA64DFR0_MTPMU_SHIFT        48
+#define ID_AA64DFR0_TRACEFILT_SHIFT    40
   #define ID_AA64DFR0_PMSVER_SHIFT    32
   #define ID_AA64DFR0_CTX_CMPS_SHIFT    28
   #define ID_AA64DFR0_WRPS_SHIFT        20

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 6338151f263c..986974be0178 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -366,6 +366,8 @@ static const struct arm64_ftr_bits ftr_id_mmfr0[] = {
   };
     static const struct arm64_ftr_bits ftr_id_aa64dfr0[] = {
+    S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_MTPMU_SHIFT, 4, 0),
+    ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64DFR0_TRACEFILT_SHIFT, 4, 0),

We maske both the fields for KVM in AArch32 ID registers. We should do the same here.

MTPMU is defined for AArch32 ID register ID_DFR1_EL1, even though the
entire register is hidden from KVM with ID_HIDDEN().

static const struct arm64_ftr_bits ftr_id_dfr1[] = {
         S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_DFR1_MTPMU_SHIFT, 4, 0),
         ARM64_FTR_END,
};

Should the ID_AA64DFR0_EL1 be hidden from KVM as well. But it has many
other existing features apart from MTPMU and TRACEFILT which are being
added here.

No, you must mask out those two fields in the emulation. Other fields 
are still relevant for guests (e.g, PMU). See, ptr-auth for e.g.

Suzuki

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