Re: [PATCH 4/5] KVM: Fix compound mmio.

[Avi Kivity <avi@redhat.com>]

On 04/12/2011 03:34 PM, Gleb Natapov wrote:
> On Tue, Apr 12, 2011 at 03:27:40PM +0300, Avi Kivity wrote:
> >  On 04/12/2011 03:22 PM, Gleb Natapov wrote:
> >  >On Tue, Apr 12, 2011 at 03:19:00PM +0300, Avi Kivity wrote:
> >  >>   On 04/12/2011 12:36 PM, Gleb Natapov wrote:
> >  >>   >mmio_index should be taken into account when copying data from
> >  >>   >userspace.
> >  >>   >
> >  >>   >Signed-off-by: Gleb Natapov<gleb@redhat.com>
> >  >>   >---
> >  >>   >    arch/x86/kvm/x86.c |    3 ++-
> >  >>   >    1 files changed, 2 insertions(+), 1 deletions(-)
> >  >>   >
> >  >>   >diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >  >>   >index b568779..609c7ab 100644
> >  >>   >--- a/arch/x86/kvm/x86.c
> >  >>   >+++ b/arch/x86/kvm/x86.c
> >  >>   >@@ -5518,7 +5518,8 @@ static int complete_mmio(struct kvm_vcpu *vcpu)
> >  >>   >    	if (vcpu->mmio_needed) {
> >  >>   >    		vcpu->mmio_needed = 0;
> >  >>   >    		if (!vcpu->mmio_is_write)
> >  >>   >-			memcpy(vcpu->mmio_data, run->mmio.data, 8);
> >  >>   >+			memcpy(vcpu->mmio_data + vcpu->mmio_index,
> >  >>   >+			       run->mmio.data, 8);
> >  >>   >    		vcpu->mmio_index += 8;
> >  >>   >    		if (vcpu->mmio_index<    vcpu->mmio_size) {
> >  >>   >    			run->exit_reason = KVM_EXIT_MMIO;
> >  >>
> >  >>   Interesting, the code passed the emulator.flat sse test.  Does it now?
> >  >>
> >  >It pass now and before. Probably by chance.
> >
> >  I don't understand how.  I explicitly set the values so that it
> >  would fail in that case.
> >
> >  Can you patch the test to fail with the current code?
> >
> If I understand correctly you've already found the explanation why
> test case worked?

Yes, but I used O_APPEND when writing my message.

> >  >But if I change read_emulated() to do
> >  >
> >  >   int n = min(size, (unsigned)KVM_MMIO_SIZE);
> >  >
> >  >instead of
> >  >
> >  >   int n = min(size, 8u);
> >  >
> >  >emulator.flat fails to emulate far jump instruction.
> >
> >  Ouch, looks like we have the multi-transaction support in two
> >  places.  I guess this is what made sse mmio work.
> >
> >  Not sure what we should do (patch is fine, question is how to
> >  resolve the duplication).
> >
> Multi-transaction works faster in complete_mmio, so read_emulated()
> should use it by doing int n = min(size, (unsigned)KVM_MMIO_SIZE).
> Other code in read_emulated() is still needed since it provides read
> re-play for multiple mmio reads during instruction emulation.

Not concerned about speed here.

Core support for large mmio feels correct, but the duplication doesn't.

-- 
error compiling committee.c: too many arguments to function