On Mon, Jun 03, 2013 at 08:30:18PM +0300, Avi Kivity wrote: > On Jun 3, 2013 7:41 PM, "Gleb Natapov" <gleb@xxxxxxxxxx> wrote: > > > > On Mon, Jun 03, 2013 at 06:42:11PM +0300, Avi Kivity wrote: > > > On Thu, May 30, 2013 at 7:34 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> > wrote: > > > > Il 30/05/2013 17:34, Paolo Bonzini ha scritto: > > > >> Il 30/05/2013 16:35, Paolo Bonzini ha scritto: > > > >>> The x86-64 extended low-byte registers were fetched correctly from > reg, > > > >>> but not from mod/rm. > > > >>> > > > >>> This fixes another bug in the boot of RHEL5.9 64-bit, but it is > still > > > >>> not enough. > > > >> > > > >> Well, it is enough but it takes 2 minutes to reach the point where > > > >> hardware virtualization is used. It is doing a lot of stuff in > > > >> emulation mode because FS and GS have leftovers from the A20 test: > > > >> > > > >> FS =0000 0000000000000000 0000ffff 00009300 DPL=0 DS16 [-WA] > > > >> GS =ffff 00000000000ffff0 0000ffff 00009300 DPL=0 DS16 [-WA] > > > >> > > > >> 0x00000000000113be: in $0x92,%al > > > >> 0x00000000000113c0: or $0x2,%al > > > >> 0x00000000000113c2: out %al,$0x92 > > > >> 0x00000000000113c4: xor %ax,%ax > > > >> 0x00000000000113c6: mov %ax,%fs > > > >> 0x00000000000113c8: dec %ax > > > >> 0x00000000000113c9: mov %ax,%gs > > > >> 0x00000000000113cb: inc %ax > > > >> 0x00000000000113cc: mov %ax,%fs:0x200 > > > >> 0x00000000000113d0: cmp %gs:0x210,%ax > > > >> 0x00000000000113d5: je 0x113cb > > > >> > > > >> The DPL < RPL test fails. Any ideas? Should we introduce a new > > > >> intermediate value for emulate_invalid_guest_state (0=none, 1=some, > 2=full)? > > > > > > > > One idea could be to replace invalid descriptors with NULL ones. Then > > > > you can intercept this in the #GP handler and trigger emulation for > that > > > > instruction only. > > > > > > Won't work, vmx won't let you enter in such a configuration. > > > > > Why? It is possible to have NULL descriptor in 32bit mode with vmx. But > > we do not usually intercept #GP while executing 32bit mode, so we will > > have to track if there is artificial NULL selector and enables #GP > > interception and then emulate on every #GP. > > Sorry, was thinking of virtual-8086 mode. It should work. > > > > > > Maybe you can detect the exact code sequence (%eip, some instructions, > > > register state) and clear %fs and %gs. > > My be we can set dpl to rpl unconditionally on a switch from 16 to 32 > > bit. The only problem I can see with it is that if a guest enters user > > mode without explicitly reload the segment it will be accessible by a > > user mode code, but I am not sure it is well defined what dpl of a 16 > > bit segment is after transition to 32 bit mode anyway, so it would be > > crazy to do so. > > The problem is you cannot detect a segment reload if you do that.Trapping > #GP preserves correctness in all cases (at the cost of some complexity). > I do not see why I would want to detect reload. Setting segment to NULL has a disadvantage that if guest will read selector it will get wrong value, but may be we can leave selector alone and mark segment unusable. I always wondered what VMX has "unusable" attribute for, may be this is it. -- Gleb. -- 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
