KVM: PPC: Book3S HV: Fix LPCR one_reg interface

Unfortunately, the LPCR got defined as a 32-bit register in the
one_reg interface.  This is unfortunate because KVM allows userspace
to control the DPFD (default prefetch depth) field, which is in the
upper 32 bits.  The result is that DPFD always get set to 0, which
reduces performance in the guest.

We can't just change KVM_REG_PPC_LPCR to be a 64-bit register ID,
since that would break existing userspace binaries.  Instead we define
a new KVM_REG_PPC_LPCR_64 id which is 64-bit.  Userspace can still use
the old KVM_REG_PPC_LPCR id, but we now only modify those fields in
the bottom 32 bits that userspace can modify (ILE, TC and AIL).
If userspace uses the new KVM_REG_PPC_LPCR_64 id, it can modify DPFD
as well.

BZ: 111438

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Paul Mackerras <paulus@samba.org>

3 files changed, 14 insertions, 3 deletions

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 8fc7971926ffe0..78d82465a04a68 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1839,7 +1839,8 @@ registers, find a list below:
   PPC   | KVM_REG_PPC_PID	| 64
   PPC   | KVM_REG_PPC_ACOP	| 64
   PPC   | KVM_REG_PPC_VRSAVE	| 32
-  PPC   | KVM_REG_PPC_LPCR	| 64
+  PPC   | KVM_REG_PPC_LPCR	| 32
+  PPC   | KVM_REG_PPC_LPCR_64	| 64
   PPC   | KVM_REG_PPC_PPR	| 64
   PPC   | KVM_REG_PPC_ARCH_COMPAT | 32
   PPC   | KVM_REG_PPC_DABRX     | 32
diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
index e45bdbfe68e24a..599153393da2f4 100644
--- a/arch/powerpc/include/uapi/asm/kvm.h
+++ b/arch/powerpc/include/uapi/asm/kvm.h
@@ -535,6 +535,7 @@ struct kvm_get_htab_header {
 
 #define KVM_REG_PPC_VRSAVE	(KVM_REG_PPC | KVM_REG_SIZE_U32 | 0xb4)
 #define KVM_REG_PPC_LPCR	(KVM_REG_PPC | KVM_REG_SIZE_U32 | 0xb5)
+#define KVM_REG_PPC_LPCR_64	(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0xb5)
 #define KVM_REG_PPC_PPR		(KVM_REG_PPC | KVM_REG_SIZE_U64 | 0xb6)
 
 /* Architecture compatibility level */
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 2bc3aee6d1b258..06486de568228b 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -858,7 +858,8 @@ static int kvm_arch_vcpu_ioctl_set_sregs_hv(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
-static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr)
+static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,
+		bool preserve_top32)
 {
 	struct kvmppc_vcore *vc = vcpu->arch.vcore;
 	u64 mask;
@@ -893,6 +894,10 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr)
 	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC;
 	if (cpu_has_feature(CPU_FTR_ARCH_207S))
 		mask |= LPCR_AIL;
+
+	/* Broken 32bit version of 32bit LPCR must not clean top bits */
+	if (preserve_top32)
+		mask &= 0xFFFFFFFF;
 	vc->lpcr = (vc->lpcr & ~mask) | (new_lpcr & mask);
 	spin_unlock(&vc->lock);
 }
@@ -1027,6 +1032,7 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 		*val = get_reg_val(id, vcpu->arch.vcore->tb_offset);
 		break;
 	case KVM_REG_PPC_LPCR:
+	case KVM_REG_PPC_LPCR_64:
 		*val = get_reg_val(id, vcpu->arch.vcore->lpcr);
 		break;
 	case KVM_REG_PPC_PPR:
@@ -1253,7 +1259,10 @@ static int kvmppc_set_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 			ALIGN(set_reg_val(id, *val), 1UL << 24);
 		break;
 	case KVM_REG_PPC_LPCR:
-		kvmppc_set_lpcr(vcpu, set_reg_val(id, *val));
+		kvmppc_set_lpcr(vcpu, set_reg_val(id, *val), true);
+		break;
+	case KVM_REG_PPC_LPCR_64:
+		kvmppc_set_lpcr(vcpu, set_reg_val(id, *val), false);
 		break;
 	case KVM_REG_PPC_PPR:
 		vcpu->arch.ppr = set_reg_val(id, *val);