From: Sean Christopherson <seanjc@google.com>
To: Anish Moorthy <amoorthy@google.com>
Cc: Oliver Upton <oliver.upton@linux.dev>,
jthoughton@google.com, kvm@vger.kernel.org
Subject: Re: [WIP Patch v2 09/14] KVM: Introduce KVM_CAP_MEMORY_FAULT_NOWAIT without implementation
Date: Fri, 17 Mar 2023 13:54:44 -0700 [thread overview]
Message-ID: <ZBTTlNrWeT9f1mjZ@google.com> (raw)
In-Reply-To: <CAF7b7mr9oJfY7Y2PQtHDRyM5-mtXYFamW3mR5_Ap8a4TjG34LQ@mail.gmail.com>
On Fri, Mar 17, 2023, Anish Moorthy wrote:
> On Fri, Mar 17, 2023 at 11:59 AM Oliver Upton <oliver.upton@linux.dev> wrote:
>
> > > + #define KVM_MEM_ABSENT_MAPPING_FAULT (1UL << 2)
> >
> > call it KVM_MEM_EXIT_ABSENT_MAPPING
> > ...
> > I'm not a fan of this architecture-specific dependency. Userspace is already
> > explicitly opting in to this behavior by way of the memslot flag. These sort
> > of exits are entirely orthogonal to the -EFAULT conversion earlier in the
> > series.
>
> I'm not a fan of the semantics varying between architectures either:
> but the reason I have it like that (and that the EFAULT conversions
> exist in this series in the first place) is (a) not having
> KVM_CAP_MEMORY_FAULT_EXIT implemented for arm and (b) Sean's following
> statement from https://lore.kernel.org/kvm/Y%2FfS0eab7GG0NVKS@google.com/
Strictly speaking, if y'all buy my argument that the flag shouldn't control the
gup behavior, there won't be semantic differences for the memslot flag. KVM will
(obviously) behavior differently if KVM_CAP_MEMORY_FAULT_EXIT is not set, but that
will hold true for x86 as well. The only difference is that x86 will also support
an orthogonal flag that makes the fast-only memslot flag useful in practice.
So yeah, there will be an arch dependency, but only because arch code needs to
actually handle perform the exit, and that's true no matter what.
That said, there's zero reason to put X86 in the name. Just add the capability
as KVM_CAP_MEMORY_FAULT_EXIT or whatever and mark it as x86 in the documentation.
next prev parent reply other threads:[~2023-03-17 20:54 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-15 2:17 [WIP Patch v2 00/14] Avoiding slow get-user-pages via memory fault exit Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 01/14] KVM: selftests: Allow many vCPUs and reader threads per UFFD in demand paging test Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 02/14] KVM: selftests: Use EPOLL in userfaultfd_util reader threads and signal errors via TEST_ASSERT Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 03/14] KVM: Allow hva_pfn_fast to resolve read-only faults Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 04/14] KVM: x86: Add KVM_CAP_X86_MEMORY_FAULT_EXIT and associated kvm_run field Anish Moorthy
2023-03-17 0:02 ` Isaku Yamahata
2023-03-17 18:33 ` Anish Moorthy
2023-03-17 19:30 ` Oliver Upton
2023-03-17 21:50 ` Sean Christopherson
2023-03-17 22:44 ` Anish Moorthy
2023-03-20 15:53 ` Sean Christopherson
2023-03-20 18:19 ` Anish Moorthy
2023-03-20 22:11 ` Anish Moorthy
2023-03-21 15:21 ` Sean Christopherson
2023-03-21 18:01 ` Anish Moorthy
2023-03-21 19:43 ` Sean Christopherson
2023-03-22 21:06 ` Anish Moorthy
2023-03-22 23:17 ` Sean Christopherson
2023-03-28 22:19 ` Anish Moorthy
2023-04-04 19:34 ` Sean Christopherson
2023-04-04 20:40 ` Anish Moorthy
2023-04-04 22:07 ` Sean Christopherson
2023-04-05 20:21 ` Anish Moorthy
2023-03-17 18:35 ` Oliver Upton
2023-03-15 2:17 ` [WIP Patch v2 05/14] KVM: x86: Implement memory fault exit for direct_map Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 06/14] KVM: x86: Implement memory fault exit for kvm_handle_page_fault Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 07/14] KVM: x86: Implement memory fault exit for setup_vmgexit_scratch Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 08/14] KVM: x86: Implement memory fault exit for FNAME(fetch) Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 09/14] KVM: Introduce KVM_CAP_MEMORY_FAULT_NOWAIT without implementation Anish Moorthy
2023-03-17 18:59 ` Oliver Upton
2023-03-17 20:15 ` Anish Moorthy
2023-03-17 20:54 ` Sean Christopherson [this message]
2023-03-17 23:42 ` Anish Moorthy
2023-03-20 15:13 ` Sean Christopherson
2023-03-20 19:53 ` Anish Moorthy
2023-03-17 20:17 ` Sean Christopherson
2023-03-20 22:22 ` Oliver Upton
2023-03-21 14:50 ` Sean Christopherson
2023-03-21 20:23 ` Oliver Upton
2023-03-21 21:01 ` Sean Christopherson
2023-03-15 2:17 ` [WIP Patch v2 10/14] KVM: x86: Implement KVM_CAP_MEMORY_FAULT_NOWAIT Anish Moorthy
2023-03-17 0:32 ` Isaku Yamahata
2023-03-15 2:17 ` [WIP Patch v2 11/14] KVM: arm64: Allow user_mem_abort to return 0 to signal a 'normal' exit Anish Moorthy
2023-03-17 18:18 ` Oliver Upton
2023-03-15 2:17 ` [WIP Patch v2 12/14] KVM: arm64: Implement KVM_CAP_MEMORY_FAULT_NOWAIT Anish Moorthy
2023-03-17 18:27 ` Oliver Upton
2023-03-17 19:00 ` Anish Moorthy
2023-03-17 19:03 ` Oliver Upton
2023-03-17 19:24 ` Sean Christopherson
2023-03-15 2:17 ` [WIP Patch v2 13/14] KVM: selftests: Add memslot_flags parameter to memstress_create_vm Anish Moorthy
2023-03-15 2:17 ` [WIP Patch v2 14/14] KVM: selftests: Handle memory fault exits in demand_paging_test Anish Moorthy
2023-03-17 17:43 ` [WIP Patch v2 00/14] Avoiding slow get-user-pages via memory fault exit Oliver Upton
2023-03-17 18:13 ` Sean Christopherson
2023-03-17 18:46 ` David Matlack
2023-03-17 18:54 ` Oliver Upton
2023-03-17 18:59 ` David Matlack
2023-03-17 19:53 ` Anish Moorthy
2023-03-17 22:03 ` Sean Christopherson
2023-03-20 15:56 ` Sean Christopherson
2023-03-17 20:35 ` Sean Christopherson
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