On Sun, Oct 03, 2010, Alexander Graf wrote about "Re: TSC in nested SVM and VMX": > Looking through the spec, the only indicator I've found is this passage: > > TSC_OFFSET - an offset to add when the guest reads the TSC (time stamp > counter). Guest writes to the TSC can be intercepted and emulated by > changing the offset (without writing the physical TSC). This offset is > cleared when the guest exits back to the host. > > So apparently writes to TSC don't affect tsc_offset, but instead affect > the host's tsc skew. So with nesting a non-intercepted tsc write affects > L1's tsc_offset. This means the code is correct. Sorry for the fuss :).
I don't understand, how does this passage imply that writes to the TSC don't affect the tsc_offset? It says that "writes to the TSC" can (I don't know why this word was used...) "changing the offset". I don't understand why a guest should be allowed to ruin its host's TSC (or in the nested case, why an L2 should be allowed to ruin L1's TSC without L1's knowledge) - isn't this exactly why the TSC offset exists? -- Nadav Har'El | Sunday, Oct 3 2010, 25 Tishri 5771 [email protected] |----------------------------------------- Phone +972-523-790466, ICQ 13349191 |"Computers are useless. They can only http://nadav.harel.org.il |give you answers." -- Pablo Picasso -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
