On Mon, Jul 09, 2012 at 02:15:37PM +0300, Avi Kivity wrote:
> On 07/09/2012 12:02 PM, Xiao Guangrong wrote:
> > After commit f78146b0f9230765c6315b2e14f56112513389ad:
> >
> > KVM: Fix page-crossing MMIO
> >
> > MMIO that are split across a page boundary are currently broken - the
> > code does not expect to be aborted by the exit to userspace for the
> > first MMIO fragment.
> >
> > This patch fixes the problem by generalizing the current code for handling
> > 16-byte MMIOs to handle a number of "fragments", and changes the MMIO
> > code to create those fragments.
> >
> > Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
> > Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> >
> > Multiple MMIO reads can be merged into mmio_fragments, the read buffer is not
> > needed anymore
> >
> > Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> > ---
> > arch/x86/include/asm/kvm_emulate.h | 1 -
> > arch/x86/kvm/emulate.c | 43 ++++-------------------------------
> > arch/x86/kvm/x86.c | 2 -
> > 3 files changed, 5 insertions(+), 41 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
> > index 1ac46c22..339d7c6 100644
> > --- a/arch/x86/include/asm/kvm_emulate.h
> > +++ b/arch/x86/include/asm/kvm_emulate.h
> > @@ -286,7 +286,6 @@ struct x86_emulate_ctxt {
> > struct operand *memopp;
> > struct fetch_cache fetch;
> > struct read_cache io_read;
> > - struct read_cache mem_read;
> > };
> >
>
> Suppose we have a RMW instruction. On the first entry to
> x86_emulate_insn() we'll drop to userspace and perform the read, and the
> seconds we'll read from the cache and complete the write.
>
> Without the read cache this cannot work.
>
Cache is needed to emulate instructions that need more than one read
that can go to MMIO.
> kvm-unit-tests.git has a test for xchg to mmio. Does it still work?
>
> I agree this code has to go, but it needs to be replaced by something.
> Maybe a .valid flag in struct operand.
>
Valid will not enough for that.
--
Gleb.
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