From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
To: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"keescook@chromium.org" <keescook@chromium.org>,
"Christopherson, Sean J" <sean.j.christopherson@intel.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"x86@kernel.org" <x86@kernel.org>,
"luto@kernel.org" <luto@kernel.org>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"Hansen, Dave" <dave.hansen@intel.com>
Cc: "kristen@linux.intel.com" <kristen@linux.intel.com>,
"Dock, Deneen T" <deneen.t.dock@intel.com>
Subject: Re: [RFC PATCH 00/13] XOM for KVM guest userspace
Date: Fri, 4 Oct 2019 19:03:58 +0000 [thread overview]
Message-ID: <8a03afd35240c180c3bea8d613acd85f8dee86cc.camel@intel.com> (raw)
In-Reply-To: <bc025a4f-2128-24ed-e5b7-76802f22cd53@redhat.com>
On Fri, 2019-10-04 at 09:22 +0200, Paolo Bonzini wrote:
> On 03/10/19 23:23, Rick Edgecombe wrote:
> > Since software would have previously received a #PF with the RSVD error code
> > set, when the HW encountered any set bits in the region 51 to M, there was
> > some
> > internal discussion on whether this should have a virtual MSR for the OS to
> > turn
> > it on only if the OS knows it isn't relying on this behavior for bit M. The
> > argument against needing an MSR is this blurb from the Intel SDM about
> > reserved
> > bits:
> > "Bits reserved in the paging-structure entries are reserved for future
> > functionality. Software developers should be aware that such bits may be
> > used in
> > the future and that a paging-structure entry that causes a page-fault
> > exception
> > on one processor might not do so in the future."
> >
> > So in the current patchset there is no MSR write required for the guest to
> > turn
> > on this feature. It will have this behavior whenever qemu is run with
> > "-cpu +xo".
>
> I think the part of the manual that you quote is out of date. Whenever
> Intel has "unreserved" bits in the page tables they have done that only
> if specific bits in CR4 or EFER or VMCS execution controls are set; this
> is a good thing, and I'd really like it to be codified in the SDM.
>
> The only bits for which this does not (and should not) apply are indeed
> bits 51:MAXPHYADDR. But the SDM makes it clear that bits 51:MAXPHYADDR
> are reserved, hence "unreserving" bits based on just a QEMU command line
> option would be against the specification. So, please don't do this and
> introduce an MSR that enables the feature.
>
> Paolo
>
Hi Paolo,
Thanks for taking a look!
Fair enough, MSR it is.
Rick
next prev parent reply other threads:[~2019-10-04 19:04 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-03 21:23 [RFC PATCH 00/13] XOM for KVM guest userspace Rick Edgecombe
2019-10-03 21:23 ` [RFC PATCH 01/13] kvm: Enable MTRR to work with GFNs with perm bits Rick Edgecombe
2019-10-14 6:47 ` Yu Zhang
2019-10-14 18:44 ` Edgecombe, Rick P
2019-10-03 21:23 ` [RFC PATCH 02/13] kvm: Add support for X86_FEATURE_KVM_XO Rick Edgecombe
2019-10-03 21:23 ` [RFC PATCH 03/13] kvm: Add XO memslot type Rick Edgecombe
2019-10-04 7:27 ` Paolo Bonzini
2019-10-04 19:06 ` Edgecombe, Rick P
2019-10-06 16:15 ` Paolo Bonzini
2019-10-03 21:23 ` [RFC PATCH 04/13] kvm, vmx: Add support for gva exit qualification Rick Edgecombe
2019-10-03 21:23 ` [RFC PATCH 05/13] kvm: Add #PF injection for KVM XO Rick Edgecombe
2019-10-04 7:42 ` Paolo Bonzini
2019-10-04 19:11 ` Edgecombe, Rick P
2019-10-03 21:23 ` [RFC PATCH 06/13] kvm: Add KVM_CAP_EXECONLY_MEM Rick Edgecombe
2019-10-04 7:24 ` Paolo Bonzini
2019-10-04 19:11 ` Edgecombe, Rick P
2019-10-03 21:23 ` [RFC PATCH 07/13] kvm: Add docs for KVM_CAP_EXECONLY_MEM Rick Edgecombe
2019-10-03 21:23 ` [RFC PATCH 08/13] x86/boot: Rename USE_EARLY_PGTABLE_L5 Rick Edgecombe
2019-10-03 21:23 ` [RFC PATCH 09/13] x86/cpufeature: Add detection of KVM XO Rick Edgecombe
2019-10-29 23:33 ` Kees Cook
2019-10-29 23:52 ` Edgecombe, Rick P
2019-10-30 14:55 ` Sean Christopherson
2019-10-30 21:02 ` Edgecombe, Rick P
2019-10-03 21:23 ` [RFC PATCH 10/13] x86/mm: Add NR page bit for " Rick Edgecombe
2019-10-04 7:33 ` Paolo Bonzini
2019-10-03 21:23 ` [RFC PATCH 11/13] x86, ptdump: Add NR bit to page table dump Rick Edgecombe
2019-10-03 21:23 ` [RFC PATCH 12/13] mmap: Add XO support for KVM XO Rick Edgecombe
2019-10-04 7:34 ` Paolo Bonzini
2019-10-04 19:12 ` Edgecombe, Rick P
2019-10-03 21:24 ` [RFC PATCH 13/13] x86/Kconfig: Add Kconfig for KVM based XO Rick Edgecombe
2019-10-29 23:36 ` Kees Cook
2019-10-30 0:01 ` Edgecombe, Rick P
2019-10-30 18:36 ` Kees Cook
2019-10-04 7:22 ` [RFC PATCH 00/13] XOM for KVM guest userspace Paolo Bonzini
2019-10-04 19:03 ` Edgecombe, Rick P [this message]
2019-10-04 14:56 ` Andy Lutomirski
2019-10-04 20:09 ` Edgecombe, Rick P
2019-10-05 1:33 ` Andy Lutomirski
2019-10-07 18:14 ` Edgecombe, Rick P
2019-10-29 23:40 ` Kees Cook
2019-10-30 0:27 ` Edgecombe, Rick P
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