Messages in this thread |  | | Date | Thu, 17 Oct 2013 10:33:33 +0100 | From | "Jan Beulich" <> | Subject | Re: [PATCH, RFC] x86-64: properly handle FPU code/data selectors |
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>>> On 17.10.13 at 11:27, Gleb Natapov <gleb@redhat.com> wrote: > On Wed, Oct 16, 2013 at 05:13:40PM +0100, Jan Beulich wrote: >> > It preserves *less* state, because the upper 32 bits of rip are now >> > corrupted. Any 64-bit application that actually looks at the FP >> > rip/rdp fields now get the WRONG VALUES. >> >> But again - this isn't being done for ordinary 64-bit applications, >> this is only happening for KVM guests. And there not being a >> protocol for telling the caller whether a certain context hold >> 64-bit offsets or selector/offset pairs shouldn't be a reason to >> think of a solution to the problem. >> > KVM knows what mode guest vcpu is in. is_long_mode(vcpu) will tell you > if it is in long mode or not. No need to guess it.
So what if that 64-bit guest OS is running a 32-bit app? You can only positively know the _current_ guest word size when the guest is not in long mode.
Jan
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