[PATCH v2] KVM: arm64: Advertise ID_AA64PFR0_EL1.CSV2/3 to protected VMs

[PATCH v2] KVM: arm64: Advertise ID_AA64PFR0_EL1.CSV2/3 to protected VMs

[Fuad Tabba]

The existing pKVM code attempts to do that using a value
initialized to 0 but never set. To advertise csv2/3 to a
protected guest, pass their values to hyp when initializing hyp's
view of guests' ID_AA64PFR0_EL1.

Similar to non-protected KVM, these are system-wide, rather than
per cpu, for simplicity.

Fixes: 6c30bfb18d0b ("KVM: arm64: Add handlers for protected VM System Registers")
Signed-off-by: Fuad Tabba <tabba@google.com>
---
 arch/arm64/kvm/arm.c                          | 24 ++++++++++++++++++-
 .../arm64/kvm/hyp/include/nvhe/fixed_config.h |  5 +++-
 arch/arm64/kvm/hyp/nvhe/sys_regs.c            |  7 ------
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 3bd732eaf087..68e8e04e1143 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1889,9 +1889,31 @@ static int __init do_pkvm_init(u32 hyp_va_bits)
 	return ret;
 }
 
+static u64 get_hyp_id_aa64pfr0_el1(void)
+{
+	u64 val = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
+
+	/*
+	 * Track whether the system isn't affected by spectre/meltown in the
+	 * hypervisor's view of id_aa64pfr0_el1, used for protected VMs.
+	 * Although this is per-CPU, we make it global for simplicity, e.g., not
+	 * to have to worry about vcpu migration.
+	 *
+	 * Unlike for non-protected VMs, userspace cannot override this for
+	 * protected VMs.
+	 */
+	val &= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_CSV2),
+		arm64_get_spectre_v2_state() == SPECTRE_UNAFFECTED);
+
+	val &= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_CSV3),
+		arm64_get_meltdown_state() == SPECTRE_UNAFFECTED);
+
+	return val;
+}
+
 static void kvm_hyp_init_symbols(void)
 {
-	kvm_nvhe_sym(id_aa64pfr0_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64PFR0_EL1);
+	kvm_nvhe_sym(id_aa64pfr0_el1_sys_val) = get_hyp_id_aa64pfr0_el1();
 	kvm_nvhe_sym(id_aa64pfr1_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64PFR1_EL1);
 	kvm_nvhe_sym(id_aa64isar0_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64ISAR0_EL1);
 	kvm_nvhe_sym(id_aa64isar1_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64ISAR1_EL1);
diff --git a/arch/arm64/kvm/hyp/include/nvhe/fixed_config.h b/arch/arm64/kvm/hyp/include/nvhe/fixed_config.h
index 07edfc7524c9..37440e1dda93 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/fixed_config.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/fixed_config.h
@@ -33,11 +33,14 @@
  * Allow for protected VMs:
  * - Floating-point and Advanced SIMD
  * - Data Independent Timing
+ * - Spectre/Meltdown Mitigation
  */
 #define PVM_ID_AA64PFR0_ALLOW (\
 	ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_FP) | \
 	ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_AdvSIMD) | \
-	ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_DIT) \
+	ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_DIT) | \
+	ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_CSV2) | \
+	ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_CSV3) \
 	)
 
 /*
diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
index 08d2b004f4b7..edd969a1f36b 100644
--- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
+++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
@@ -85,19 +85,12 @@ static u64 get_restricted_features_unsigned(u64 sys_reg_val,
 
 static u64 get_pvm_id_aa64pfr0(const struct kvm_vcpu *vcpu)
 {
-	const struct kvm *kvm = (const struct kvm *)kern_hyp_va(vcpu->kvm);
 	u64 set_mask = 0;
 	u64 allow_mask = PVM_ID_AA64PFR0_ALLOW;
 
 	set_mask |= get_restricted_features_unsigned(id_aa64pfr0_el1_sys_val,
 		PVM_ID_AA64PFR0_RESTRICT_UNSIGNED);
 
-	/* Spectre and Meltdown mitigation in KVM */
-	set_mask |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_CSV2),
-			       (u64)kvm->arch.pfr0_csv2);
-	set_mask |= FIELD_PREP(ARM64_FEATURE_MASK(ID_AA64PFR0_EL1_CSV3),
-			       (u64)kvm->arch.pfr0_csv3);
-
 	return (id_aa64pfr0_el1_sys_val & allow_mask) | set_mask;
 }
 

base-commit: 96a4627dbbd48144a65af936b321701c70876026
-- 
2.40.0.348.gf938b09366-goog

Re: [PATCH v2] KVM: arm64: Advertise ID_AA64PFR0_EL1.CSV2/3 to protected VMs

[Marc Zyngier]

On Thu, 30 Mar 2023 11:17:38 +0100,
Fuad Tabba <tabba@google.com> wrote:
> 
> The existing pKVM code attempts to do that using a value
> initialized to 0 but never set. To advertise csv2/3 to a
> protected guest, pass their values to hyp when initializing hyp's
> view of guests' ID_AA64PFR0_EL1.
> 
> Similar to non-protected KVM, these are system-wide, rather than
> per cpu, for simplicity.
> 
> Fixes: 6c30bfb18d0b ("KVM: arm64: Add handlers for protected VM System Registers")
> Signed-off-by: Fuad Tabba <tabba@google.com>

Reviewed-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.