On Sat, Nov 10, 2012 at 03:43:49PM +0000, Christoffer Dall wrote: > When the guest accesses I/O memory this will create data abort > exceptions and they are handled by decoding the HSR information > (physical address, read/write, length, register) and forwarding reads > and writes to QEMU which performs the device emulation. > > Certain classes of load/store operations do not support the syndrome > information provided in the HSR and we therefore must be able to fetch > the offending instruction from guest memory and decode it manually. > > We only support instruction decoding for valid reasonable MMIO operations > where trapping them do not provide sufficient information in the HSR (no > 16-bit Thumb instructions provide register writeback that we care about). > > The following instruction types are NOT supported for MMIO operations > despite the HSR not containing decode info: > - any Load/Store multiple > - any load/store exclusive > - any load/store dual > - anything with the PC as the dest register > > This requires changing the general flow somewhat since new calls to run > the VCPU must check if there's a pending MMIO load and perform the write > after userspace has made the data available. > > Rusty Russell fixed a horrible race pointed out by Ben Herrenschmidt: > (1) Guest complicated mmio instruction traps. > (2) The hardware doesn't tell us enough, so we need to read the actual > instruction which was being exectuted. > (3) KVM maps the instruction virtual address to a physical address. > (4) The guest (SMP) swaps out that page, and fills it with something else. > (5) We read the physical address, but now that's the wrong thing. > > Reviewed-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> > Signed-off-by: Rusty Russell <rusty.russell@xxxxxxxxxx> > Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> > Signed-off-by: Christoffer Dall <c.dall@xxxxxxxxxxxxxxxxxxxxxx> This is looking like the right sort of thing now, but I would like to see an Acked-by from Dave [CC'd] for this patch. I'll try and hit the vGIC code this week... Thanks, Will -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
