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KVM: PPC: Book3S PR: Make instruction fetch fallback work for system calls

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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: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
This commit is contained in:
Paul Mackerras 2013-08-06 14:15:19 +10:00 committed by Alexander Graf
parent 9d1ffdd8f3
commit 8b23de2948
2 changed files with 39 additions and 1 deletions
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38
arch/powerpc/include/asm/kvm_book3s.h
View File

@ -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;

2
arch/powerpc/kvm/book3s_pr.c
View File

@ -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);