On 07/05/15 13:51, Nicholas Mc Guire wrote: > Currently if kvm_mips_complete_mmio_load() fails with EMULATE_FAIL it will > not role back the pc nor will the caller handle this failure. > > Signed-off-by: Nicholas Mc Guire <[email protected]> > --- > arch/mips/kvm/emulate.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > kvm_mips_complete_mmio_load is called only in arch/mips/kvm/mips.c without > checking the return value to signal EMULATE_FAIL: > 383 if (vcpu->mmio_needed) { > 384 if (!vcpu->mmio_is_write) > 385 kvm_mips_complete_mmio_load(vcpu, run); > 386 vcpu->mmio_needed = 0; > 387 } > > so maybe kvm_mips_complete_mmio_load should role back in case of failure > at arch/mips/kvm/emuilate.c:kvm_mips_complete_mmio_load() > 2406 if (er == EMULATE_FAIL) { > 2408 return er; > > something like the below patch - only based no looking at how EMULATE_FAIL > is handled at other locations - not sure if this is appropriate here. > > Patch was only compile tested msp71xx_defconfig + CONFIG_KVM=m > > Patch is against 4.1-rc2 (localversion-next is -next-20150506) > > diff --git a/arch/mips/kvm/emulate.c b/arch/mips/kvm/emulate.c > index 2f0fc60..b58596b 100644 > --- a/arch/mips/kvm/emulate.c > +++ b/arch/mips/kvm/emulate.c > @@ -2403,8 +2403,10 @@ enum emulation_result > kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, > */ > curr_pc = vcpu->arch.pc; > er = update_pc(vcpu, vcpu->arch.pending_load_cause); > - if (er == EMULATE_FAIL) > + if (er == EMULATE_FAIL) { > + vcpu->arch.pc = curr_pc;
If update_pc returns EMULATE_FAIL then vcpu->arch.pc won't have been
modified, so putting it back to the old value is redundant.
Actually, curr_pc can be dropped from this function since nothing else
can go wrong that would cause the PC to need rolling back. Effectively
kvm_mips_emulate_load() has omitted to update the PC since it'll only
return to userland to handle the MMIO and get the load data, so by the
time it gets back to kvm_mips_complete_mmio_load(), it already has
everything it needs to guarantee success.
Cheers
James
> return er;
> + }
>
> switch (run->mmio.len) {
> case 4:
>
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