[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH]Fix the bug of guest os installationfailure and win2k boot failure
On 18/3/08 09:35, "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx> wrote: > Do you mean that in a multi-thread process, one thread issues an I/O > operation, and in the time slot that just after the processor has fetched the > instruction, validated the access, but before Xen re-fetches the instruction > for emulation, another thread steals that I/O instruction and replace it with > a new one? Maybe we can regard it as a kind of attack... We could regard it as that, since that is what it would be. :-) > This could be happen in theory, but I think other instruction emulation > may also have this problem. Which other instruction emulations? Can you give an example? > In your last sentence, do you mean that we still > need to do an entire I/O permission check (including CPL, IOPL, and TSS I/O > bitmap) in x86_emulate() for safety consideration? Thanks! :-) Yes. Like I said: the CPL-IOPL check is very cheap, the TSS bitmap check is a little more expensive but probably relatively rare. And in any case the I/O port access latency is largely dominated by the VMEXIT/VMENTRY times. Also the devices we emulate are mostly managed by mmio. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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