On 18/11/15 09:12, Wu, Feng wrote: > >> -----Original Message----- >> From: xen-devel-boun...@lists.xen.org [mailto:xen-devel- >> boun...@lists.xen.org] On Behalf Of Jan Beulich >> Sent: Tuesday, November 17, 2015 6:26 PM >> To: Andrew Cooper <andrew.coop...@citrix.com> >> Cc: Tian, Kevin <kevin.t...@intel.com>; wei.l...@citrix.com; >> ian.campb...@citrix.com; stefano.stabell...@eu.citrix.com; >> george.dun...@eu.citrix.com; ian.jack...@eu.citrix.com; xen- >> de...@lists.xen.org; Nakajima, Jun <jun.nakaj...@intel.com>; Han, >> Huaitong <huaitong....@intel.com>; k...@xen.org >> Subject: Re: [Xen-devel] [PATCH 00/10] x86/hvm: pkeys, add memory >> protection-key support >> >>>>> On 16.11.15 at 18:45, <andrew.coop...@citrix.com> wrote: >>> Furthermore, it is unclear (given the unwritten ABI) whether it is even >>> safe to move _PAGE_GNTTAB out of the way, as this is visible to a PV guest. >> It seems pretty clear to me that this would be unsafe: It being >> part of L1_DISALLOW_MASK, if it moved and a guest used the >> bit for its own purposes, the guest would break. I guess we'll >> need an ELF note by which the guest can advertise which of the >> available bits it doesn't care about itself. > Actually, we don't expose this feature to PV guest, we only expose it > to HVM. In that case, is there still issues like you discussed above?
You have turned on CR4.PKE, and _PAGE_GNTTAB is bit 62 in a PTE. Futhermore, you don't prevent/audit a PV guest's use of the PK bits. This makes it usable by PV guests, even if the feature isn't advertised. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
