From: Oliver Upton <oliver.upton@linux.dev>
To: Sean Christopherson <seanjc@google.com>
Cc: James Houghton <jthoughton@google.com>,
Anish Moorthy <amoorthy@google.com>,
kvm@vger.kernel.org, kvmarm@lists.linux.dev, pbonzini@redhat.com,
maz@kernel.org, robert.hoo.linux@gmail.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 v6 06/14] KVM: Add memslot flag to let userspace force an exit on missing hva mappings
Date: Fri, 2 Feb 2024 01:01:34 +0000 [thread overview]
Message-ID: <Zbw-7sxotjX3xWsO@linux.dev> (raw)
In-Reply-To: <ZbvGoz67L3gtnHhI@google.com>
On Thu, Feb 01, 2024 at 08:28:19AM -0800, Sean Christopherson wrote:
[...]
> Yeah, I let's just make KVM_EXIT_ON_MISSING mutually exclusive with
> KVM_MEM_READONLY. KVM (oviously) honors the primary MMU protections, so userspace
> can (and does) map read-only memory into the guest without READONLY. As Oliver
> pointed out, making the *memslot* RO is intended for use cases where userspace
> wants writes to be treated like emulated MMIO.
Well, it was clear enough to me what open source VMMs are doing, I was
curious if Google's VMM is doing something strange with RO memslots that
made the optimization desirable. But it sounds like we're all in
agreement that RO memslots aren't consequential for post-copy.
> We can always add support in the future in the extremely unlikely event someone
> comes along with a legitimate reason for KVM_EXIT_ON_MISSING to play nice with
> KVM_MEM_READONLY.
+1, the less stupid things we let userspace do the better.
--
Thanks,
Oliver
next prev parent reply other threads:[~2024-02-02 1:01 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-09 21:03 [PATCH v6 00/14] Improve KVM + userfaultfd performance via KVM_MEMORY_FAULT_EXITs on stage-2 faults Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 01/14] KVM: Documentation: Clarify meaning of hva_to_pfn()'s 'atomic' parameter Anish Moorthy
2024-02-07 15:26 ` Sean Christopherson
2024-02-07 18:44 ` Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 02/14] KVM: Documentation: Add docstrings for __kvm_read/write_guest_page() Anish Moorthy
2024-02-07 15:30 ` Sean Christopherson
2023-11-09 21:03 ` [PATCH v6 03/14] KVM: Simplify error handling in __gfn_to_pfn_memslot() Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 04/14] KVM: Define and communicate KVM_EXIT_MEMORY_FAULT RWX flags to userspace Anish Moorthy
2024-02-07 15:30 ` Sean Christopherson
2024-02-07 18:57 ` Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 05/14] KVM: Try using fast GUP to resolve read faults Anish Moorthy
2024-02-05 21:55 ` Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 06/14] KVM: Add memslot flag to let userspace force an exit on missing hva mappings Anish Moorthy
2024-01-31 0:25 ` James Houghton
2024-01-31 21:59 ` Anish Moorthy
2024-02-01 0:26 ` James Houghton
2024-02-01 1:19 ` Oliver Upton
2024-02-01 16:28 ` Sean Christopherson
2024-02-01 19:24 ` Anish Moorthy
2024-02-02 1:03 ` Oliver Upton
2024-02-02 1:01 ` Oliver Upton [this message]
2024-02-01 16:09 ` Sean Christopherson
2024-02-01 19:53 ` Anish Moorthy
2024-02-07 15:35 ` Sean Christopherson
2023-11-09 21:03 ` [PATCH v6 07/14] KVM: x86: Enable KVM_CAP_EXIT_ON_MISSING and annotate EFAULTs from stage-2 fault handler Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 08/14] KVM: arm64: Enable KVM_CAP_MEMORY_FAULT_INFO Anish Moorthy
2023-11-09 21:07 ` Anish Moorthy
2024-02-07 15:39 ` Sean Christopherson
2024-02-07 16:41 ` Oliver Upton
2024-02-07 21:21 ` Anish Moorthy
2024-02-07 21:41 ` Sean Christopherson
2024-02-07 22:07 ` Oliver Upton
2024-02-09 1:13 ` Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 09/14] KVM: arm64: Enable KVM_CAP_EXIT_ON_MISSING and annotate an EFAULT from stage-2 fault-handler Anish Moorthy
2024-01-30 23:58 ` James Houghton
2024-01-31 22:38 ` Anish Moorthy
2024-02-09 1:21 ` Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 10/14] KVM: selftests: Report per-vcpu demand paging rate from demand paging test Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 11/14] KVM: selftests: Allow many vCPUs and reader threads per UFFD in " Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 12/14] KVM: selftests: Use EPOLL in userfaultfd_util reader threads and signal errors via TEST_ASSERT Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 13/14] KVM: selftests: Add memslot_flags parameter to memstress_create_vm() Anish Moorthy
2023-11-09 21:03 ` [PATCH v6 14/14] KVM: selftests: Handle memory fault exits in demand_paging_test Anish Moorthy
2024-02-07 15:46 ` [PATCH v6 00/14] Improve KVM + userfaultfd performance via KVM_MEMORY_FAULT_EXITs on stage-2 faults Sean Christopherson
2024-02-09 16:00 ` Anish Moorthy
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