From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [PATCH 6/8] xen/x86: Calculate PV CR4 masks at boot Date: Thu, 25 Jun 2015 14:40:44 +0100 Message-ID: <558C20FC0200007800089AEC@mail.emea.novell.com> References: <1435163500-10589-1-git-send-email-andrew.cooper3@citrix.com> <1435163500-10589-7-git-send-email-andrew.cooper3@citrix.com> <558C19840200007800089A5D@mail.emea.novell.com> <558C02CE.2030208@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <558C02CE.2030208@citrix.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andrew Cooper Cc: Xen-devel List-Id: xen-devel@lists.xenproject.org >>> On 25.06.15 at 15:31, wrote: > On 25/06/15 14:08, Jan Beulich wrote: >>>>> On 24.06.15 at 18:31, wrote: >>> --- a/xen/arch/x86/domain.c >>> +++ b/xen/arch/x86/domain.c >>> @@ -682,24 +682,47 @@ void arch_domain_unpause(struct domain *d) >>> viridian_time_ref_count_thaw(d); >>> } >>> >>> -unsigned long pv_guest_cr4_fixup(const struct vcpu *v, unsigned long guest_cr4) >>> +/* >>> + * These are the masks of CR4 bits (subject to hardware availability) which a >>> + * PV guest may not legitimiately attempt to modify. >>> + */ >>> +static unsigned long __read_mostly pv_cr4_mask, compat_pv_cr4_mask; >> The patch generally being fine, I still wonder why you chose to use >> "pv" in the names instead of the previous "hv": To me, the latter >> makes more sense: "the bits the hypervisor controls" instead of "the >> bits pv guests do not control". > > It is the set of bits Xen doesn't mind the guest attempting to modify, It's the inverse of that set of bits really, isn't it? Jan > which is specifically different from the bits Xen actually controls, and > different from the set of bits shadowed in a guests CR4. > > The masks do represent a superset of the shadowed bits, (clamped by > hardware support). Bits such as PGE and FSGSBASE are deemed ok for a > guest to attempt to modify, but are not shadowed and the guests > interests are completely ignored. > > ~Andrew