From: Elliot Berman <quic_eberman@quicinc.com>
To: Ackerley Tng <ackerleytng@google.com>,
Sean Christopherson <seanjc@google.com>
Cc: <pbonzini@redhat.com>, <maz@kernel.org>, <oliver.upton@linux.dev>,
<chenhuacai@kernel.org>, <mpe@ellerman.id.au>,
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<wei.w.wang@intel.com>, <liam.merwick@oracle.com>,
<isaku.yamahata@gmail.com>, <kirill.shutemov@linux.intel.com>
Subject: Re: [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory
Date: Mon, 28 Aug 2023 19:53:26 -0700 [thread overview]
Message-ID: <253965df-6d80-bbfd-ab01-f9e69b274bf3@quicinc.com> (raw)
In-Reply-To: <diqzttsiu67n.fsf@ackerleytng-ctop.c.googlers.com>
On 8/28/2023 3:56 PM, Ackerley Tng wrote:
> 1. Since the physical memory's representation is the inode and should be
> coupled to the virtual machine (as a concept, not struct kvm), should
> the binding/coupling be with the file, or the inode?
>
I've been working on Gunyah's implementation in parallel (not yet posted
anywhere). Thus far, I've coupled the virtual machine struct to the
struct file so that I can increment the file refcount when mapping the
gmem to the virtual machine.
> 2. Should struct kvm still be bound to the file/inode at gmem file
> creation time, since
>
> + struct kvm isn't a good representation of a "virtual machine"
> + we currently don't have anything that really represents a "virtual
> machine" without hardware support
>
>
> I'd also like to bring up another userspace use case that Google has:
> re-use of gmem files for rebooting guests when the KVM instance is
> destroyed and rebuilt.
>
> When rebooting a VM there are some steps relating to gmem that are
> performance-sensitive:
>
> a. Zeroing pages from the old VM when we close a gmem file/inode
> b. Deallocating pages from the old VM when we close a gmem file/inode
> c. Allocating pages for the new VM from the new gmem file/inode
> d. Zeroing pages on page allocation
>
> We want to reuse the gmem file to save re-allocating pages (b. and c.),
> and one of the two page zeroing allocations (a. or d.).
>
> Binding the gmem file to a struct kvm on creation time means the gmem
> file can't be reused with another VM on reboot. Also, host userspace is
> forced to close the gmem file to allow the old VM to be freed.
>
> For other places where files pin KVM, like the stats fd pinning vCPUs, I
> guess that matters less since there isn't much of a penalty to close and
> re-open the stats fd.
I had a 3rd question that's related to how to wire the gmem up to a
virtual machine:
I learned of a usecase to implement copy-on-write for gmem. The premise
would be to have a "golden copy" of the memory that multiple virtual
machines can map in as RO. If a virtual machine tries to write to those
pages, they get copied to a virtual machine-specific page that isn't
shared with other VMs. How do we track those pages?
Thanks,
Elliot
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next prev parent reply other threads:[~2023-08-29 2:54 UTC|newest]
Thread overview: 131+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-18 23:44 [RFC PATCH v11 00/29] KVM: guest_memfd() and per-page attributes Sean Christopherson
2023-07-18 23:44 ` [RFC PATCH v11 01/29] KVM: Wrap kvm_gfn_range.pte in a per-action union Sean Christopherson
2023-07-19 13:39 ` Jarkko Sakkinen
2023-07-19 15:39 ` Sean Christopherson
2023-07-19 16:55 ` Paolo Bonzini
2023-07-26 20:22 ` Sean Christopherson
2023-07-21 6:26 ` Yan Zhao
2023-07-21 10:45 ` Xu Yilun
2023-07-25 18:05 ` Sean Christopherson
2023-07-18 23:44 ` [RFC PATCH v11 02/29] KVM: Tweak kvm_hva_range and hva_handler_t to allow reusing for gfn ranges Sean Christopherson
2023-07-19 17:12 ` Paolo Bonzini
2023-07-18 23:44 ` [RFC PATCH v11 03/29] KVM: Use gfn instead of hva for mmu_notifier_retry Sean Christopherson
2023-07-19 17:12 ` Paolo Bonzini
2023-07-18 23:44 ` [RFC PATCH v11 04/29] KVM: PPC: Drop dead code related to KVM_ARCH_WANT_MMU_NOTIFIER Sean Christopherson
2023-07-19 17:34 ` Paolo Bonzini
2023-07-18 23:44 ` [RFC PATCH v11 05/29] KVM: Convert KVM_ARCH_WANT_MMU_NOTIFIER to CONFIG_KVM_GENERIC_MMU_NOTIFIER Sean Christopherson
2023-07-19 7:31 ` Yuan Yao
2023-07-19 14:15 ` Sean Christopherson
2023-07-20 1:15 ` Yuan Yao
2023-07-18 23:44 ` [RFC PATCH v11 06/29] KVM: Introduce KVM_SET_USER_MEMORY_REGION2 Sean Christopherson
2023-07-21 9:03 ` Paolo Bonzini
2023-07-28 9:25 ` Quentin Perret
2023-07-29 0:03 ` Sean Christopherson
2023-07-31 9:30 ` Quentin Perret
2023-07-31 15:58 ` Paolo Bonzini
2023-07-18 23:44 ` [RFC PATCH v11 07/29] KVM: Add KVM_EXIT_MEMORY_FAULT exit Sean Christopherson
2023-07-19 7:54 ` Yuan Yao
2023-07-19 14:16 ` Sean Christopherson
2023-07-18 23:44 ` [RFC PATCH v11 08/29] KVM: Introduce per-page memory attributes Sean Christopherson
2023-07-20 8:09 ` Yuan Yao
2023-07-20 19:02 ` Isaku Yamahata
2023-07-20 20:20 ` Sean Christopherson
2023-07-21 10:57 ` Paolo Bonzini
2023-07-21 15:56 ` Xiaoyao Li
2023-07-24 4:43 ` Xu Yilun
2023-07-26 15:59 ` Sean Christopherson
2023-07-27 3:24 ` Xu Yilun
2023-08-02 20:31 ` Isaku Yamahata
2023-08-14 0:44 ` Binbin Wu
2023-08-14 21:54 ` Sean Christopherson
2023-07-18 23:44 ` [RFC PATCH v11 09/29] KVM: x86: Disallow hugepages when memory attributes are mixed Sean Christopherson
2023-07-21 11:59 ` Paolo Bonzini
2023-07-21 17:41 ` Sean Christopherson
2023-07-18 23:44 ` [RFC PATCH v11 10/29] mm: Add AS_UNMOVABLE to mark mapping as completely unmovable Sean Christopherson
2023-07-25 10:24 ` Kirill A . Shutemov
2023-07-25 12:51 ` Matthew Wilcox
2023-07-26 11:36 ` Kirill A . Shutemov
2023-07-28 16:02 ` Vlastimil Babka
2023-07-28 16:13 ` Paolo Bonzini
2023-09-01 8:23 ` Vlastimil Babka
2023-07-18 23:44 ` [RFC PATCH v11 11/29] security: Export security_inode_init_security_anon() for use by KVM Sean Christopherson
2023-07-19 2:14 ` Paul Moore
2023-07-31 10:46 ` Vlastimil Babka
2023-07-18 23:44 ` [RFC PATCH v11 12/29] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory Sean Christopherson
2023-07-19 17:21 ` Vishal Annapurve
2023-07-19 17:47 ` Sean Christopherson
2023-07-20 14:45 ` Xiaoyao Li
2023-07-20 15:14 ` Sean Christopherson
2023-07-20 21:28 ` Isaku Yamahata
2023-07-21 6:13 ` Yuan Yao
2023-07-21 22:27 ` Isaku Yamahata
2023-07-21 22:33 ` Sean Christopherson
2023-07-21 15:05 ` Xiaoyao Li
2023-07-21 15:42 ` Xiaoyao Li
2023-07-21 17:42 ` Sean Christopherson
2023-07-21 17:17 ` Paolo Bonzini
2023-07-21 17:50 ` Sean Christopherson
2023-07-25 15:09 ` Wang, Wei W
2023-07-25 16:03 ` Sean Christopherson
2023-07-26 1:51 ` Wang, Wei W
2023-07-31 16:23 ` Fuad Tabba
2023-07-26 17:18 ` Elliot Berman
2023-07-26 19:28 ` Sean Christopherson
2023-07-27 10:39 ` Fuad Tabba
2023-07-27 17:13 ` Sean Christopherson
2023-07-31 13:46 ` Fuad Tabba
2023-08-03 19:15 ` Ryan Afranji
2023-08-07 23:06 ` Ackerley Tng
2023-08-08 21:13 ` Sean Christopherson
2023-08-10 23:57 ` Vishal Annapurve
2023-08-11 17:44 ` Sean Christopherson
2023-08-15 18:43 ` Ackerley Tng
2023-08-15 20:03 ` Sean Christopherson
2023-08-21 17:30 ` Ackerley Tng
2023-08-21 19:33 ` Sean Christopherson
2023-08-28 22:56 ` Ackerley Tng
2023-08-29 2:53 ` Elliot Berman [this message]
2023-09-14 19:12 ` Sean Christopherson
2023-09-14 18:15 ` Sean Christopherson
2023-09-14 23:19 ` Ackerley Tng
2023-09-15 0:33 ` Sean Christopherson
2023-08-30 15:12 ` Binbin Wu
2023-08-30 16:44 ` Ackerley Tng
2023-09-01 3:45 ` Binbin Wu
2023-09-01 16:46 ` Ackerley Tng
2023-07-18 23:44 ` [RFC PATCH v11 13/29] KVM: Add transparent hugepage support for dedicated guest memory Sean Christopherson
2023-07-21 15:07 ` Paolo Bonzini
2023-07-21 17:13 ` Sean Christopherson
2023-09-06 22:10 ` Paolo Bonzini
2023-07-18 23:44 ` [RFC PATCH v11 14/29] KVM: x86/mmu: Handle page fault for private memory Sean Christopherson
2023-07-21 15:09 ` Paolo Bonzini
2023-07-18 23:44 ` [RFC PATCH v11 15/29] KVM: Drop superfluous __KVM_VCPU_MULTIPLE_ADDRESS_SPACE macro Sean Christopherson
2023-07-21 15:07 ` Paolo Bonzini
2023-07-18 23:44 ` [RFC PATCH v11 16/29] KVM: Allow arch code to track number of memslot address spaces per VM Sean Christopherson
2023-07-21 15:12 ` Paolo Bonzini
2023-07-18 23:45 ` [RFC PATCH v11 17/29] KVM: x86: Add support for "protected VMs" that can utilize private memory Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 18/29] KVM: selftests: Drop unused kvm_userspace_memory_region_find() helper Sean Christopherson
2023-07-21 15:14 ` Paolo Bonzini
2023-07-18 23:45 ` [RFC PATCH v11 19/29] KVM: selftests: Convert lib's mem regions to KVM_SET_USER_MEMORY_REGION2 Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 20/29] KVM: selftests: Add support for creating private memslots Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 21/29] KVM: selftests: Add helpers to convert guest memory b/w private and shared Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 22/29] KVM: selftests: Add helpers to do KVM_HC_MAP_GPA_RANGE hypercalls (x86) Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 23/29] KVM: selftests: Introduce VM "shape" to allow tests to specify the VM type Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 24/29] KVM: selftests: Add GUEST_SYNC[1-6] macros for synchronizing more data Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 25/29] KVM: selftests: Add x86-only selftest for private memory conversions Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 26/29] KVM: selftests: Add KVM_SET_USER_MEMORY_REGION2 helper Sean Christopherson
2023-07-18 23:45 ` [RFC PATCH v11 27/29] KVM: selftests: Expand set_memory_region_test to validate guest_memfd() Sean Christopherson
2023-08-07 23:17 ` Ackerley Tng
2023-07-18 23:45 ` [RFC PATCH v11 28/29] KVM: selftests: Add basic selftest for guest_memfd() Sean Christopherson
2023-08-07 23:20 ` Ackerley Tng
2023-08-18 23:03 ` Sean Christopherson
2023-08-07 23:25 ` Ackerley Tng
2023-08-18 23:01 ` Sean Christopherson
2023-08-21 19:49 ` Ackerley Tng
2023-07-18 23:45 ` [RFC PATCH v11 29/29] KVM: selftests: Test KVM exit behavior for private memory/access Sean Christopherson
2023-07-24 6:38 ` [RFC PATCH v11 00/29] KVM: guest_memfd() and per-page attributes Nikunj A. Dadhania
2023-07-24 17:00 ` Sean Christopherson
2023-07-26 11:20 ` Nikunj A. Dadhania
2023-07-26 14:24 ` Sean Christopherson
2023-07-27 6:42 ` Nikunj A. Dadhania
2023-08-03 11:03 ` Vlastimil Babka
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