On Thu, Jun 23, 2016 at 06:03:01PM +0200, Paolo Bonzini wrote: > > > On 18/06/2016 11:01, Quentin Casasnovas wrote: > > Cross-checking the KVM/VMX VMREAD emulation code with the Intel Software > > Developper Manual Volume 3C - "VMREAD - Read Field from Virtual-Machine > > Control Structure", I found that we're enforcing that the destination > > operand is NOT located in a read-only data segment or any code segment when > > the L1 is in long mode - BUT that check should only happen when it is in > > protected mode. > > > > Shuffling the code a bit to make our emulation follow the specification > > allows me to boot a Xen dom0 in a nested KVM and start HVM L2 guests > > without problems. > > That's great, and I'm applying the patch, but it's also pretty weird. :) > Do you have a pointer to Xen source code that does a VMREAD into a > read-only data segment or a code segment?
It is indeed pretty weird. Looking at the Xen stack trace, it looks like the vmread is writing to an on-stack buffer, and surely it must be writable so I wonder if Xen might not be using an executable stack for some reason? That would be a bit scary so I'm surely missing something. Is there an easy way to know from my KVM host the different segment permission setup by the guest? Quentin
