From: Sean Christopherson <seanjc@google.com>
To: Anish Moorthy <amoorthy@google.com>
Cc: oliver.upton@linux.dev, maz@kernel.org, kvm@vger.kernel.org,
kvmarm@lists.linux.dev, robert.hoo.linux@gmail.com,
jthoughton@google.com, dmatlack@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: Fri, 8 Mar 2024 14:07:13 -0800 [thread overview]
Message-ID: <ZeuMEdQTFADDSFkX@google.com> (raw)
In-Reply-To: <20240215235405.368539-7-amoorthy@google.com>
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.
2. What is your best guess as to when KVM userfault patches will be available,
even if only in RFC form?
The reason I ask is because Oliver pointed out (off-list) that (a) Google is the
primary user for KVM_MEM_EXIT_ON_MISSING, possibly the _only_ user for the
forseeable future, and (b) if Google moves on to KVM userfault before ever
ingesting KVM_MEM_EXIT_ON_MISSING from upstream, then we'll have effectively
added dead code to KVM's eternal ABI.
next prev parent reply other threads:[~2024-03-08 22:07 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 [this message]
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
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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