KVM: PPC: Fetch prefixed instructions from the guest

In order to handle emulation of prefixed instructions in the guest,
this first makes vcpu->arch.last_inst be an unsigned long, i.e. 64
bits on 64-bit platforms.  For prefixed instructions, the upper 32
bits are used for the prefix and the lower 32 bits for the suffix, and
both halves are byte-swapped if the guest endianness differs from the
host.

Next, vcpu->arch.emul_inst is now 64 bits wide, to match the HEIR
register on POWER10.  Like HEIR, for a prefixed instruction it is
defined to have the prefix is in the top 32 bits and the suffix in the
bottom 32 bits, with both halves in the correct byte order.

kvmppc_get_last_inst is extended on 64-bit machines to put the prefix
and suffix in the right places in the ppc_inst_t being returned.

kvmppc_load_last_inst now returns the instruction in an unsigned long
in the same format as vcpu->arch.last_inst.  It makes the decision
about whether to fetch a suffix based on the SRR1_PREFIXED bit in the
MSR image stored in the vcpu struct, which generally comes from SRR1
or HSRR1 on an interrupt.  This bit is defined in Power ISA v3.1B to
be set if the interrupt occurred due to a prefixed instruction and
cleared otherwise for all interrupts except for instruction storage
interrupt, which does not come to the hypervisor.  It is set to zero
for asynchronous interrupts such as external interrupts.  In previous
ISA versions it was always set to 0 for all interrupts except
instruction storage interrupt.

The code in book3s_hv_rmhandlers.S that loads the faulting instruction
on a HDSI is only used on POWER8 and therefore doesn't ever need to
load a suffix.

[npiggin@gmail.com - check that the is-prefixed bit in SRR1 matches the
type of instruction that was fetched.]

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/ZAgsq9h1CCzouQuV@cleo

1 files changed, 24 insertions, 8 deletions

diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
index d703d1b3ba7e..bc57d058ad5b 100644
--- a/arch/powerpc/include/asm/kvm_ppc.h
+++ b/arch/powerpc/include/asm/kvm_ppc.h
@@ -85,7 +85,8 @@ extern int kvmppc_handle_vsx_store(struct kvm_vcpu *vcpu,
 				int is_default_endian);
 
 extern int kvmppc_load_last_inst(struct kvm_vcpu *vcpu,
-				 enum instruction_fetch_type type, u32 *inst);
+				 enum instruction_fetch_type type,
+				 unsigned long *inst);
 
 extern int kvmppc_ld(struct kvm_vcpu *vcpu, ulong *eaddr, int size, void *ptr,
 		     bool data);
@@ -336,15 +337,30 @@ static inline int kvmppc_get_last_inst(struct kvm_vcpu *vcpu,
 		ret = kvmppc_load_last_inst(vcpu, type, &vcpu->arch.last_inst);
 
 	/*  Write fetch_failed unswapped if the fetch failed */
-	if (ret == EMULATE_DONE)
-		fetched_inst = kvmppc_need_byteswap(vcpu) ?
-				swab32(vcpu->arch.last_inst) :
-				vcpu->arch.last_inst;
-	else
-		fetched_inst = vcpu->arch.last_inst;
+	if (ret != EMULATE_DONE) {
+		*inst = ppc_inst(KVM_INST_FETCH_FAILED);
+		return ret;
+	}
+
+#ifdef CONFIG_PPC64
+	/* Is this a prefixed instruction? */
+	if ((vcpu->arch.last_inst >> 32) != 0) {
+		u32 prefix = vcpu->arch.last_inst >> 32;
+		u32 suffix = vcpu->arch.last_inst;
+		if (kvmppc_need_byteswap(vcpu)) {
+			prefix = swab32(prefix);
+			suffix = swab32(suffix);
+		}
+		*inst = ppc_inst_prefix(prefix, suffix);
+		return EMULATE_DONE;
+	}
+#endif
 
+	fetched_inst = kvmppc_need_byteswap(vcpu) ?
+		swab32(vcpu->arch.last_inst) :
+		vcpu->arch.last_inst;
 	*inst = ppc_inst(fetched_inst);
-	return ret;
+	return EMULATE_DONE;
 }
 
 static inline bool is_kvmppc_hv_enabled(struct kvm *kvm)