> Am 01.04.2014 um 01:03 schrieb Scott Wood <scottwood@xxxxxxxxxxxxx>: > >> On Mon, 2014-03-31 at 15:41 +0200, Alexander Graf wrote: >>> On 03/26/2014 10:17 PM, Scott Wood wrote: >>>> On Thu, 2014-02-20 at 18:30 +0200, Mihai Caraman wrote: >>>> + /* >>>> + * Another thread may rewrite the TLB entry in parallel, don't >>>> + * execute from the address if the execute permission is not set >>>> + */ >> >> What happens when another thread rewrites the TLB entry in parallel? >> Does tlbsx succeed? Does it fail? Do we see failure indicated somehow? >> Are the contents of the MAS registers consistent at this point or >> inconsistent? > > If another thread rewrites the TLB entry, then we use the new TLB entry, > just as if it had raced in hardware. This check ensures that we don't > execute from the new TLB entry if it doesn't have execute permissions > (just as hardware would). > > What happens if the new TLB entry is valid and executable, and the > instruction pointed to is valid, but doesn't trap (and thus we don't > have emulation for it)? > >> There has to be a good way to detect such a race and deal with it, no? > > How would you detect it? We don't get any information from the trap > about what physical address the instruction was fetched from, or what > the instruction was. Ah, this is a guest race where the guest modifies exactly the TLB in question. I see. Why would this ever happen in practice (in a case where we're not executing malicious code)? Alex > > -Scott > > -- 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
