Messages in this thread Patch in this message | | | Subject | Re: [PATCH v2 3/3] kvm: svm: Use the hardware provided GPA instead of page walk | From | Brijesh Singh <> | Date | Wed, 14 Dec 2016 12:39:01 -0600 |
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On 12/14/2016 11:23 AM, Paolo Bonzini wrote: > > > On 14/12/2016 18:07, Brijesh Singh wrote: >>> >> >> Since now we are going to perform multiple conditional checks before >> concluding that its safe to use HW provided GPA. How about if we add two >> functions "emulator_is_rep_string_op" and "emulator_is_two_mem_op" into >> emulator.c and use these functions inside the x86.c to determine if its >> safe to use HW provided gpa? > > Why not export only emulator_can_use_gpa from emulate.c? (So in the end > leaving emulator_is_string_op in emulate.c was the right thing to do, it > was just the test that was wrong :)). >
Actually, I was not sure if putting emulator_can_use_gpa() in emulate.c was right thing - mainly because emulator.c does not deal with GPA. I will go with your advice and put it in emulator.c, it makes easy :)
> The patch below is still missing the check for cross-page MMIO. Your > reference to the BKDG only covers MMCONFIG (sometimes referred to as > ECAM), not MMIO in general. Doing AND or OR into video memory for > example is perfectly legal, and I'm fairly sure that some obscure legacy > software does PUSH/POP into vram as well! > >
I used your below code snippet to detect cross-page MMIO access. After applying these changes cross-page MMIO read/write unit test is passing just fine. I will include it in patch.
> Actually there is a nice trick you can do to support cross-page > MMIO access detection:
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 37cd31645d45..754d251dc611 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4549,6 +4549,7 @@ static int emulator_read_write_onepage(unsigned long addr, void *val, */ if (vcpu->arch.gpa_available && !emulator_can_use_hw_gpa(ctxt) && + (addr & ~PAGE_MASK) == (exception->address & ~PAGE_MASK) && vcpu_is_mmio_gpa(vcpu, addr, exception->address, write)) { gpa = exception->address; goto mmio;
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