KVM: PPC: Book3S HV: Add a function to filter guest LPCR bits

Guest LPCR depends on hardware type, and future changes will add
restrictions based on errata and guest MMU mode. Move this logic
to a common function and use it for the cases where the guest
wants to update its LPCR (or the LPCR of a nested guest).

This also adds a warning in other places that set or update LPCR
if we try to set something that would have been disallowed by
the filter, as a sanity check.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210412014845.1517916-4-npiggin@gmail.com

2 files changed, 57 insertions, 19 deletions

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 208a053c9adf..268e31c7e49c 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1635,6 +1635,35 @@ static int kvm_arch_vcpu_ioctl_set_sregs_hv(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+/*
+ * Enforce limits on guest LPCR values based on hardware availability,
+ * guest configuration, and possibly hypervisor support and security
+ * concerns.
+ */
+unsigned long kvmppc_filter_lpcr_hv(struct kvm *kvm, unsigned long lpcr)
+{
+	/* On POWER8 and above, userspace can modify AIL */
+	if (!cpu_has_feature(CPU_FTR_ARCH_207S))
+		lpcr &= ~LPCR_AIL;
+
+	/*
+	 * On POWER9, allow userspace to enable large decrementer for the
+	 * guest, whether or not the host has it enabled.
+	 */
+	if (!cpu_has_feature(CPU_FTR_ARCH_300))
+		lpcr &= ~LPCR_LD;
+
+	return lpcr;
+}
+
+static void verify_lpcr(struct kvm *kvm, unsigned long lpcr)
+{
+	if (lpcr != kvmppc_filter_lpcr_hv(kvm, lpcr)) {
+		WARN_ONCE(1, "lpcr 0x%lx differs from filtered 0x%lx\n",
+			  lpcr, kvmppc_filter_lpcr_hv(kvm, lpcr));
+	}
+}
+
 static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
 		bool preserve_top32)
 {
@@ -1643,6 +1672,23 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
 	u64 mask;
 
 	spin_lock(&vc->lock);
+
+	/*
+	 * Userspace can only modify
+	 * DPFD (default prefetch depth), ILE (interrupt little-endian),
+	 * TC (translation control), AIL (alternate interrupt location),
+	 * LD (large decrementer).
+	 * These are subject to restrictions from kvmppc_filter_lcpr_hv().
+	 */
+	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC | LPCR_AIL | LPCR_LD;
+
+	/* Broken 32-bit version of LPCR must not clear top bits */
+	if (preserve_top32)
+		mask &= 0xFFFFFFFF;
+
+	new_lpcr = kvmppc_filter_lpcr_hv(kvm,
+			(vc->lpcr & ~mask) | (new_lpcr & mask));
+
 	/*
 	 * If ILE (interrupt little-endian) has changed, update the
 	 * MSR_LE bit in the intr_msr for each vcpu in this vcore.
@@ -1661,25 +1707,8 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
 		}
 	}
 
-	/*
-	 * Userspace can only modify DPFD (default prefetch depth),
-	 * ILE (interrupt little-endian) and TC (translation control).
-	 * On POWER8 and POWER9 userspace can also modify AIL (alt. interrupt loc.).
-	 */
-	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC;
-	if (cpu_has_feature(CPU_FTR_ARCH_207S))
-		mask |= LPCR_AIL;
-	/*
-	 * On POWER9, allow userspace to enable large decrementer for the
-	 * guest, whether or not the host has it enabled.
-	 */
-	if (cpu_has_feature(CPU_FTR_ARCH_300))
-		mask |= LPCR_LD;
+	vc->lpcr = new_lpcr;
 
-	/* Broken 32-bit version of LPCR must not clear top bits */
-	if (preserve_top32)
-		mask &= 0xFFFFFFFF;
-	vc->lpcr = (vc->lpcr & ~mask) | (new_lpcr & mask);
 	spin_unlock(&vc->lock);
 }
 
@@ -4644,8 +4673,10 @@ void kvmppc_update_lpcr(struct kvm *kvm, unsigned long lpcr, unsigned long mask)
 		struct kvmppc_vcore *vc = kvm->arch.vcores[i];
 		if (!vc)
 			continue;
+
 		spin_lock(&vc->lock);
 		vc->lpcr = (vc->lpcr & ~mask) | lpcr;
+		verify_lpcr(kvm, vc->lpcr);
 		spin_unlock(&vc->lock);
 		if (++cores_done >= kvm->arch.online_vcores)
 			break;
@@ -4973,6 +5004,7 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm)
 		kvmppc_setup_partition_table(kvm);
 	}
 
+	verify_lpcr(kvm, lpcr);
 	kvm->arch.lpcr = lpcr;
 
 	/* Initialization for future HPT resizes */
diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index 3060e5deffc8..d14fe32f167b 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -151,7 +151,13 @@ static void sanitise_hv_regs(struct kvm_vcpu *vcpu, struct hv_guest_state *hr)
 	 */
 	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC | LPCR_AIL | LPCR_LD |
 		LPCR_LPES | LPCR_MER;
-	hr->lpcr = (vc->lpcr & ~mask) | (hr->lpcr & mask);
+
+	/*
+	 * Additional filtering is required depending on hardware
+	 * and configuration.
+	 */
+	hr->lpcr = kvmppc_filter_lpcr_hv(vcpu->kvm,
+			(vc->lpcr & ~mask) | (hr->lpcr & mask));
 
 	/*
 	 * Don't let L1 enable features for L2 which we've disabled for L1,