[for-4.19 0/2] backport "KVM: arm64: limit PMU version to PMUv3 for ARMv8.1"

We need to backport patch #1 as well because it introduced a helper used
by patch #2.

Andrew Murray (2):
  arm64: cpufeature: Extract capped perfmon fields
  KVM: arm64: limit PMU version to PMUv3 for ARMv8.1

 arch/arm64/include/asm/cpufeature.h | 23 +++++++++++++++++++++++
 arch/arm64/include/asm/sysreg.h     |  6 ++++++
 arch/arm64/kvm/sys_regs.c           | 10 ++++++++++
 3 files changed, 39 insertions(+)

-- 
2.33.0

From: Andrew Murray <redacted>

commit 8e35aa642ee4dab01b16cc4b2df59d1936f3b3c2 upstream.

When emulating ID registers there is often a need to cap the version
bits of a feature such that the guest will not use features that the
host is not aware of. For example, when KVM mediates access to the PMU
by emulating register accesses.

Let's add a helper that extracts a performance monitors ID field and
caps the version to a given value.

Fields that identify the version of the Performance Monitors Extension
do not follow the standard ID scheme, and instead follow the scheme
described in ARM DDI 0487E.a page D13-2825 "Alternative ID scheme used
for the Performance Monitors Extension version". The value 0xF means an
IMPLEMENTATION DEFINED PMU is present, and values 0x0-OxE can be treated
the same as an unsigned field with 0x0 meaning no PMU is present.

Signed-off-by: Andrew Murray <redacted>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
[Mark: rework to handle perfmon fields]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 arch/arm64/include/asm/cpufeature.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 05f41d8f7db3..a3cc478d2570 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h

@@ -422,6 +422,29 @@ cpuid_feature_extract_unsigned_field(u64 features, int field)
 	return cpuid_feature_extract_unsigned_field_width(features, field, 4);
 }
 
+/*
+ * Fields that identify the version of the Performance Monitors Extension do
+ * not follow the standard ID scheme. See ARM DDI 0487E.a page D13-2825,
+ * "Alternative ID scheme used for the Performance Monitors Extension version".
+ */
+static inline u64 __attribute_const__
+cpuid_feature_cap_perfmon_field(u64 features, int field, u64 cap)
+{
+	u64 val = cpuid_feature_extract_unsigned_field(features, field);
+	u64 mask = GENMASK_ULL(field + 3, field);
+
+	/* Treat IMPLEMENTATION DEFINED functionality as unimplemented */
+	if (val == 0xf)
+		val = 0;
+
+	if (val > cap) {
+		features &= ~mask;
+		features |= (cap << field) & mask;
+	}
+
+	return features;
+}
+
 static inline u64 arm64_ftr_mask(const struct arm64_ftr_bits *ftrp)
 {
 	return (u64)GENMASK(ftrp->shift + ftrp->width - 1, ftrp->shift);

-- 
2.33.0

From: Andrew Murray <redacted>

commit c854188ea01062f5a5fd7f05658feb1863774eaa upstream.

We currently expose the PMU version of the host to the guest via
emulation of the DFR0_EL1 and AA64DFR0_EL1 debug feature registers.
However many of the features offered beyond PMUv3 for 8.1 are not
supported in KVM. Examples of this include support for the PMMIR
registers (added in PMUv3 for ARMv8.4) and 64-bit event counters
added in (PMUv3 for ARMv8.5).

Let's trap the Debug Feature Registers in order to limit
PMUVer/PerfMon in the Debug Feature Registers to PMUv3 for ARMv8.1
to avoid unexpected behaviour.

Both ID_AA64DFR0.PMUVer and ID_DFR0.PerfMon follow the "Alternative ID
scheme used for the Performance Monitors Extension version" where 0xF
means an IMPLEMENTATION DEFINED PMU is implemented, and values 0x0-0xE
are treated as with an unsigned field (with 0x0 meaning no PMU is
present). As we don't expect to expose an IMPLEMENTATION DEFINED PMU,
and our cap is below 0xF, we can treat these fields as unsigned when
applying the cap.

Signed-off-by: Andrew Murray <redacted>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
[Mark: make field names consistent, use perfmon cap]
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
[yuzenghui@huawei.com: adjust the context in read_id_reg()]
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 arch/arm64/include/asm/sysreg.h |  6 ++++++
 arch/arm64/kvm/sys_regs.c       | 10 ++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 22266c7e2cc1..0a8342de5796 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h

@@ -622,6 +622,12 @@
 #define ID_AA64DFR0_TRACEVER_SHIFT	4
 #define ID_AA64DFR0_DEBUGVER_SHIFT	0
 
+#define ID_AA64DFR0_PMUVER_8_1		0x4
+
+#define ID_DFR0_PERFMON_SHIFT		24
+
+#define ID_DFR0_PERFMON_8_1		0x4
+
 #define ID_ISAR5_RDM_SHIFT		24
 #define ID_ISAR5_CRC32_SHIFT		16
 #define ID_ISAR5_SHA2_SHIFT		12

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index f06629bf2be1..2799e7e9915a 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c

@@ -1049,6 +1049,16 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
 			kvm_debug("LORegions unsupported for guests, suppressing\n");
 
 		val &= ~(0xfUL << ID_AA64MMFR1_LOR_SHIFT);
+	} else if (id == SYS_ID_AA64DFR0_EL1) {
+		/* Limit guests to PMUv3 for ARMv8.1 */
+		val = cpuid_feature_cap_perfmon_field(val,
+						ID_AA64DFR0_PMUVER_SHIFT,
+						ID_AA64DFR0_PMUVER_8_1);
+	} else if (id == SYS_ID_DFR0_EL1) {
+		/* Limit guests to PMUv3 for ARMv8.1 */
+		val = cpuid_feature_cap_perfmon_field(val,
+						ID_DFR0_PERFMON_SHIFT,
+						ID_DFR0_PERFMON_8_1);
 	}
 
 	return val;

-- 
2.33.0

On Tue, Nov 28, 2023 at 03:46:31PM +0800, Zenghui Yu wrote:

We need to backport patch #1 as well because it introduced a helper used
by patch #2.

Andrew Murray (2):
  arm64: cpufeature: Extract capped perfmon fields
  KVM: arm64: limit PMU version to PMUv3 for ARMv8.1

We can not just take these in an old stable tree and not newer ones as
that would mean you could upgrade and have a regression.  Please provide
backports for all applicable stable trees and we will be glad to take
them.

thanks,

greg k-h

On 2023/11/28 16:12, Greg KH wrote:

On Tue, Nov 28, 2023 at 03:46:31PM +0800, Zenghui Yu wrote:

quoted

We need to backport patch #1 as well because it introduced a helper used
by patch #2.

Andrew Murray (2):
  arm64: cpufeature: Extract capped perfmon fields
  KVM: arm64: limit PMU version to PMUv3 for ARMv8.1

We can not just take these in an old stable tree and not newer ones as
that would mean you could upgrade and have a regression.  Please provide
backports for all applicable stable trees and we will be glad to take
them.

Thanks for the heads up! "for-5.4" patches sent now.

Zenghui

On Tue, Nov 28, 2023 at 08:00:08PM +0800, Zenghui Yu wrote:

On 2023/11/28 16:12, Greg KH wrote:

quoted

On Tue, Nov 28, 2023 at 03:46:31PM +0800, Zenghui Yu wrote:

quoted

We need to backport patch #1 as well because it introduced a helper used
by patch #2.

Andrew Murray (2):
  arm64: cpufeature: Extract capped perfmon fields
  KVM: arm64: limit PMU version to PMUv3 for ARMv8.1

We can not just take these in an old stable tree and not newer ones as
that would mean you could upgrade and have a regression.  Please provide
backports for all applicable stable trees and we will be glad to take
them.

Thanks for the heads up! "for-5.4" patches sent now.

Great, all now queued up, thanks.

greg k-h