| Message ID | 1431003091-30161-1-git-send-email-hofrat@osadl.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <hofrat@osadl.org> > --- > 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: >
On Fri, 08 May 2015, James Hogan wrote: > 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 <hofrat@osadl.org> > > --- > > 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. > ok - got it - the comment then was really missleading as it suggested that a roleback was actually needed - so in that case the curr_pc; is really an unused variable and can be tossed out - patch in a minute. thx! hofrat -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; return er; + } switch (run->mmio.len) { case 4:
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 <hofrat@osadl.org> --- 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)