On 07/27/2011 12:26 PM, Gleb Natapov wrote: > On Wed, Jul 27, 2011 at 09:47:52AM +0800, Xiao Guangrong wrote: >> On 07/26/2011 08:27 PM, Gleb Natapov wrote: >>> On Tue, Jul 26, 2011 at 07:26:46PM +0800, Xiao Guangrong wrote: >>>> We usually use repeat string instructions to clear the page, for example, >>> By "we" do you mean Linux guest? >>> >> >> I do not know other guests except linux, but, generally rep instruction is >> not used to update a page table which is been using. >> >>>> we call memset to clear a page table, stosb is used in this function, and >>>> repeated for 1024 times, that means we should occupy mmu lock for 1024 times >>>> and walking shadow page cache for 1024 times, it is terrible >>>> >>>> In fact, if it is the repeat string instructions emulated and it is not a >>>> IO/MMIO access, we can zap all the corresponding shadow pages and return to the >>>> guest, then the mapping can became writable and directly write the page >>>> >> >> >>> So this patch does two independent things as far as I can see. First it >>> stops reentering guest if rep instruction is done on memory and second >> >> No. >> Oppositely, it enters guest as soon as possible if rep instruction is done >> on memory ;-) > Oops. Indeed. I read it other way around. So why not just return > X86EMUL_UNHANDLEABLE from emulator_write_emulated_onepage() which should > have the same effect? > It seams not, the count register(RCX) is not decreased, and redundant work need to be done by handling EMULATION_FAILED. So, emulator_write_emulated_onepage() is not a good place i think. :-) -- 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
