On 01/12/2012 12:12 PM, Gleb Natapov wrote: > On Wed, Jan 11, 2012 at 06:53:31PM +0200, Nadav Amit wrote: > > Consider the case in which an instruction emulation writeback is performed > > on a page boundary. > > In such case, if a #PF occurs on the second page, the write to the first > > page already occurred and cannot be retracted. > > Therefore, validation of the second page access must be performed prior to > > writeback. > > > > Signed-off-by: Nadav Amit <[email protected]> > > --- > > arch/x86/kvm/x86.c | 13 +++++++++++++ > > 1 files changed, 13 insertions(+), 0 deletions(-) > > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > index 05fd3d7..7af3d67 100644 > > --- a/arch/x86/kvm/x86.c > > +++ b/arch/x86/kvm/x86.c > > @@ -3626,6 +3626,8 @@ struct read_write_emulator_ops { > > int bytes, void *val); > > int (*read_write_exit_mmio)(struct kvm_vcpu *vcpu, gpa_t gpa, > > void *val, int bytes); > > + gpa_t (*read_write_validate)(struct kvm_vcpu *vcpu, gva_t gva, > > + struct x86_exception *exception); > > bool write; > > }; > > > > @@ -3686,6 +3688,7 @@ static struct read_write_emulator_ops write_emultor = > > { > > .read_write_emulate = write_emulate, > > .read_write_mmio = write_mmio, > > .read_write_exit_mmio = write_exit_mmio, > > + .read_write_validate = kvm_mmu_gva_to_gpa_write, > > .write = true, > > }; > > > > @@ -3750,6 +3753,16 @@ int emulator_read_write(struct x86_emulate_ctxt > > *ctxt, unsigned long addr, > > int rc, now; > > > > now = -addr & ~PAGE_MASK; > > + > > + /* First check there is no page-fault on the next page */ > > + if (ops->read_write_validate && > > + ops->read_write_validate(vcpu, addr+now, exception) == > > + UNMAPPED_GVA) { > > + /* #PF on the first page should be reported first */ > > + ops->read_write_validate(vcpu, addr, exception); > > + return X86EMUL_PROPAGATE_FAULT; > > + } > > + > This undoes optimization that vcpu_mmio_gva_to_gpa() has for handling > mmio.
Right. I suggest changing I/O to have two phases: first, translate the virtual address into an array of two physical addresses; check exceptions and report. Then do the actual writes. > Furthermore for common (non faulting) case we will check page > tables twice on each write that crosses page boundary, first time here > and second time in emulator_read_write_onepage(). Those should be very uncommon. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
