From: Anish Moorthy <amoorthy@google.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Oliver Upton <oliver.upton@linux.dev>,
David Matlack <dmatlack@google.com>,
maz@kernel.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev,
robert.hoo.linux@gmail.com, jthoughton@google.com,
axelrasmussen@google.com, peterx@redhat.com,
nadav.amit@gmail.com, isaku.yamahata@gmail.com,
kconsul@linux.vnet.ibm.com
Subject: Re: [PATCH v7 06/14] KVM: Add memslot flag to let userspace force an exit on missing hva mappings
Date: Mon, 11 Mar 2024 10:08:56 -0700 [thread overview]
Message-ID: <CAF7b7mpgeLJudcT9YhjQOqsXxz07Y9PY1a-F0ts6oVsVJwrnpA@mail.gmail.com> (raw)
In-Reply-To: <Ze8y-vGzbDSLP-2G@google.com>
On Sun, Mar 10, 2024 at 9:46 PM Oliver Upton <oliver.upton@linux.dev> wrote:
>
> Hey,
>
> Thanks Sean for bringing this up on the list, didn't have time for a lot
> of upstream stuffs :)
>
> On Fri, Mar 08, 2024 at 04:46:32PM -0800, David Matlack wrote:
> > On 2024-03-08 02:07 PM, Sean Christopherson wrote:
> > > On Thu, Feb 15, 2024, Anish Moorthy wrote:
> > > > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > > > index 9f5d45c49e36..bf7bc21d56ac 100644
> > > > --- a/Documentation/virt/kvm/api.rst
> > > > +++ b/Documentation/virt/kvm/api.rst
> > > > @@ -1353,6 +1353,7 @@ yet and must be cleared on entry.
> > > > #define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0)
> > > > #define KVM_MEM_READONLY (1UL << 1)
> > > > #define KVM_MEM_GUEST_MEMFD (1UL << 2)
> > > > + #define KVM_MEM_EXIT_ON_MISSING (1UL << 3)
> > >
> > > David M.,
> > >
> > > Before this gets queued anywhere, a few questions related to the generic KVM
> > > userfault stuff you're working on:
> > >
> > > 1. Do you anticipate reusing KVM_MEM_EXIT_ON_MISSING to communicate that a vCPU
> > > should exit to userspace, even for guest_memfd? Or are you envisioning the
> > > "data invalid" gfn attribute as being a superset?
> > >
> > > We danced very close to this topic in the PUCK call, but I don't _think_ we
> > > ever explicitly talked about whether or not KVM_MEM_EXIT_ON_MISSING would
> > > effectively be obsoleted by a KVM_SET_MEMORY_ATTRIBUTES-based "invalid data"
> > > flag.
> > >
> > > I was originally thinking that KVM_MEM_EXIT_ON_MISSING would be re-used,
> > > but after re-watching parts of the PUCK recording, e.g. about decoupling
> > > KVM from userspace page tables, I suspect past me was wrong.
> >
> > No I don't anticipate reusing KVM_MEM_EXIT_ON_MISSING.
> >
> > The plan is to introduce a new gfn attribute and exit to userspace based
> > on that. I do forsee having an on/off switch for the new attribute, but
> > it wouldn't make sense to reuse KVM_MEM_EXIT_ON_MISSING for that.
>
> With that in mind, unless someone else has a usecase for the
> KVM_MEM_EXIT_ON_MISSING behavior my *strong* preference is that we not
> take this bit of the series upstream. The "memory fault" UAPI should
> still be useful when the KVM userfault stuff comes along.
>
> Anish, apologies, you must have whiplash from all the bikeshedding,
> nitpicking, and other fun you've been put through on this series. Thanks
> for being patient.
No worries- I got a lot of patient (and much-needed) review as well
:). And I understand not wanting to add an eternal feature when
something better is coming down the line.
On Mon, Mar 11, 2024 at 9:36 AM Sean Christopherson <seanjc@google.com> wrote:
>
> Oh, and I'll plan on grabbing patches 1-4 for 6.10.
I think patches 10/11/12 are useful changes to the selftest that make
sense to merge even with KVM_MEM_EXIT_ON_MISSING being mothballed-
they should rebase without any issues. And the annotations on the
stage-2 fault handlers seem like they should still be added, but I
suppose David can do that with his series.
next prev parent reply other threads:[~2024-03-11 17:09 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-15 23:53 [PATCH v7 00/14] Improve KVM + userfaultfd performance via KVM_EXIT_MEMORY_FAULTs on stage-2 faults Anish Moorthy
2024-02-15 23:53 ` [PATCH v7 01/14] KVM: Clarify meaning of hva_to_pfn()'s 'atomic' parameter Anish Moorthy
2024-02-15 23:53 ` [PATCH v7 02/14] KVM: Add function comments for __kvm_read/write_guest_page() Anish Moorthy
2024-02-15 23:53 ` [PATCH v7 03/14] KVM: Documentation: Make note of the KVM_MEM_GUEST_MEMFD memslot flag Anish Moorthy
2024-04-09 22:47 ` Sean Christopherson
2024-02-15 23:53 ` [PATCH v7 04/14] KVM: Simplify error handling in __gfn_to_pfn_memslot() Anish Moorthy
2024-04-09 22:44 ` Sean Christopherson
2024-02-15 23:53 ` [PATCH v7 05/14] KVM: Define and communicate KVM_EXIT_MEMORY_FAULT RWX flags to userspace Anish Moorthy
2024-02-15 23:53 ` [PATCH v7 06/14] KVM: Add memslot flag to let userspace force an exit on missing hva mappings Anish Moorthy
2024-03-08 22:07 ` Sean Christopherson
2024-03-09 0:46 ` David Matlack
2024-03-11 4:45 ` Oliver Upton
2024-03-11 16:20 ` David Matlack
2024-03-11 16:36 ` Sean Christopherson
2024-03-11 17:08 ` Anish Moorthy [this message]
2024-03-11 21:21 ` Oliver Upton
2024-02-15 23:53 ` [PATCH v7 07/14] KVM: x86: Enable KVM_CAP_EXIT_ON_MISSING and annotate EFAULTs from stage-2 fault handler Anish Moorthy
2024-02-15 23:53 ` [PATCH v7 08/14] KVM: arm64: Enable KVM_CAP_MEMORY_FAULT_INFO and annotate fault in the " Anish Moorthy
2024-03-04 20:00 ` Oliver Upton
2024-03-04 20:10 ` Oliver Upton
2024-03-04 20:32 ` Sean Christopherson
2024-03-04 21:03 ` Oliver Upton
2024-03-04 22:49 ` Sean Christopherson
2024-03-05 1:01 ` Oliver Upton
2024-03-05 15:39 ` Sean Christopherson
2024-02-15 23:54 ` [PATCH v7 09/14] KVM: arm64: Implement and advertise KVM_CAP_EXIT_ON_MISSING Anish Moorthy
2024-02-15 23:54 ` [PATCH v7 10/14] KVM: selftests: Report per-vcpu demand paging rate from demand paging test Anish Moorthy
2024-04-09 22:49 ` Sean Christopherson
2024-02-15 23:54 ` [PATCH v7 11/14] KVM: selftests: Allow many vCPUs and reader threads per UFFD in " Anish Moorthy
2024-04-09 22:58 ` Sean Christopherson
2024-02-15 23:54 ` [PATCH v7 12/14] KVM: selftests: Use EPOLL in userfaultfd_util reader threads and signal errors via TEST_ASSERT Anish Moorthy
2024-02-15 23:54 ` [PATCH v7 13/14] KVM: selftests: Add memslot_flags parameter to memstress_create_vm() Anish Moorthy
2024-02-15 23:54 ` [PATCH v7 14/14] KVM: selftests: Handle memory fault exits in demand_paging_test Anish Moorthy
2024-02-16 7:36 ` [PATCH v7 00/14] Improve KVM + userfaultfd performance via KVM_EXIT_MEMORY_FAULTs on stage-2 faults Gupta, Pankaj
2024-02-16 20:00 ` Anish Moorthy
2024-02-16 23:40 ` Axel Rasmussen
2024-02-21 7:35 ` Gupta, Pankaj
2024-04-10 0:19 ` Sean Christopherson
2024-05-07 17:38 ` Anish Moorthy
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