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Commit 8b23de29 authored by Paul Mackerras's avatar Paul Mackerras Committed by Alexander Graf
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KVM: PPC: Book3S PR: Make instruction fetch fallback work for system calls 



It turns out that if we exit the guest due to a hcall instruction (sc 1),
and the loading of the instruction in the guest exit path fails for any
reason, the call to kvmppc_ld() in kvmppc_get_last_inst() fetches the
instruction after the hcall instruction rather than the hcall itself.
This in turn means that the instruction doesn't get recognized as an
hcall in kvmppc_handle_exit_pr() but gets passed to the guest kernel
as a sc instruction.  That usually results in the guest kernel getting
a return code of 38 (ENOSYS) from an hcall, which often triggers a
BUG_ON() or other failure.

This fixes the problem by adding a new variant of kvmppc_get_last_inst()
called kvmppc_get_last_sc(), which fetches the instruction if necessary
from pc - 4 rather than pc.

Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
parent 9d1ffdd8

arch/powerpc/include/asm/kvm_book3s.h

+38 −0
Original line number Diff line number Diff line
@@ -334,6 +334,27 @@ static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu) 
	return r;

}



/*

 * Like kvmppc_get_last_inst(), but for fetching a sc instruction.

 * Because the sc instruction sets SRR0 to point to the following

 * instruction, we have to fetch from pc - 4.

 */

static inline u32 kvmppc_get_last_sc(struct kvm_vcpu *vcpu)

{

	ulong pc = kvmppc_get_pc(vcpu) - 4;

	struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);

	u32 r;



	/* Load the instruction manually if it failed to do so in the

	 * exit path */

	if (svcpu->last_inst == KVM_INST_FETCH_FAILED)

		kvmppc_ld(vcpu, &pc, sizeof(u32), &svcpu->last_inst, false);



	r = svcpu->last_inst;

	svcpu_put(svcpu);

	return r;

}



static inline ulong kvmppc_get_fault_dar(struct kvm_vcpu *vcpu)

{

	struct kvmppc_book3s_shadow_vcpu *svcpu = svcpu_get(vcpu);
@@ -446,6 +467,23 @@ static inline u32 kvmppc_get_last_inst(struct kvm_vcpu *vcpu) 
	return vcpu->arch.last_inst;

}



/*

 * Like kvmppc_get_last_inst(), but for fetching a sc instruction.

 * Because the sc instruction sets SRR0 to point to the following

 * instruction, we have to fetch from pc - 4.

 */

static inline u32 kvmppc_get_last_sc(struct kvm_vcpu *vcpu)

{

	ulong pc = kvmppc_get_pc(vcpu) - 4;



	/* Load the instruction manually if it failed to do so in the

	 * exit path */

	if (vcpu->arch.last_inst == KVM_INST_FETCH_FAILED)

		kvmppc_ld(vcpu, &pc, sizeof(u32), &vcpu->arch.last_inst, false);



	return vcpu->arch.last_inst;

}



static inline ulong kvmppc_get_fault_dar(struct kvm_vcpu *vcpu)

{

	return vcpu->arch.fault_dar;

arch/powerpc/kvm/book3s_pr.c

+1 −1
Original line number Diff line number Diff line
@@ -792,7 +792,7 @@ program_interrupt: 
	}

	case BOOK3S_INTERRUPT_SYSCALL:

		if (vcpu->arch.papr_enabled &&

		    (kvmppc_get_last_inst(vcpu) == 0x44000022) &&

		    (kvmppc_get_last_sc(vcpu) == 0x44000022) &&

		    !(vcpu->arch.shared->msr & MSR_PR)) {

			/* SC 1 papr hypercalls */

			ulong cmd = kvmppc_get_gpr(vcpu, 3);