From: Paolo Bonzini <pbonzini@redhat.com>
To: Ben Gardon <bgardon@google.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Peter Xu <peterx@redhat.com>,
Sean Christopherson <seanjc@google.com>,
Peter Shier <pshier@google.com>,
Junaid Shahid <junaids@google.com>,
Jim Mattson <jmattson@google.com>,
Yulei Zhang <yulei.kernel@gmail.com>,
Wanpeng Li <kernellwp@gmail.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Xiao Guangrong <xiaoguangrong.eric@gmail.com>
Subject: Re: [PATCH v2 0/7] Lazily allocate memslot rmaps
Date: Mon, 3 May 2021 15:44:56 +0200 [thread overview]
Message-ID: <a3279647-fb30-4033-2a9d-75d473bd8f8e@redhat.com> (raw)
In-Reply-To: <20210429211833.3361994-1-bgardon@google.com>
On 29/04/21 23:18, Ben Gardon wrote:
> This series enables KVM to save memory when using the TDP MMU by waiting
> to allocate memslot rmaps until they are needed. To do this, KVM tracks
> whether or not a shadow root has been allocated. In order to get away
> with not allocating the rmaps, KVM must also be sure to skip operations
> which iterate over the rmaps. If the TDP MMU is in use and we have not
> allocated a shadow root, these operations would essentially be op-ops
> anyway. Skipping the rmap operations has a secondary benefit of avoiding
> acquiring the MMU lock in write mode in many cases, substantially
> reducing MMU lock contention.
>
> This series was tested on an Intel Skylake machine. With the TDP MMU off
> and on, this introduced no new failures on kvm-unit-tests or KVM selftests.
Thanks, I only reported some technicalities in the ordering of loads
(which matter since the loads happen with SRCU protection only). Apart
from this, this looks fine!
Paolo
> Changelog:
> v2:
> Incorporated feedback from Paolo and Sean
> Replaced the memslot_assignment_lock with slots_arch_lock, which
> has a larger critical section.
>
> Ben Gardon (7):
> KVM: x86/mmu: Track if shadow MMU active
> KVM: x86/mmu: Skip rmap operations if shadow MMU inactive
> KVM: x86/mmu: Deduplicate rmap freeing
> KVM: x86/mmu: Factor out allocating memslot rmap
> KVM: mmu: Refactor memslot copy
> KVM: mmu: Add slots_arch_lock for memslot arch fields
> KVM: x86/mmu: Lazily allocate memslot rmaps
>
> arch/x86/include/asm/kvm_host.h | 13 +++
> arch/x86/kvm/mmu/mmu.c | 153 +++++++++++++++++++++-----------
> arch/x86/kvm/mmu/mmu_internal.h | 2 +
> arch/x86/kvm/mmu/tdp_mmu.c | 6 +-
> arch/x86/kvm/mmu/tdp_mmu.h | 4 +-
> arch/x86/kvm/x86.c | 110 +++++++++++++++++++----
> include/linux/kvm_host.h | 9 ++
> virt/kvm/kvm_main.c | 54 ++++++++---
> 8 files changed, 264 insertions(+), 87 deletions(-)
>
next prev parent reply other threads:[~2021-05-03 13:45 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 21:18 [PATCH v2 0/7] Lazily allocate memslot rmaps Ben Gardon
2021-04-29 21:18 ` [PATCH v2 1/7] KVM: x86/mmu: Track if shadow MMU active Ben Gardon
2021-05-03 13:42 ` Paolo Bonzini
2021-05-04 17:26 ` Ben Gardon
2021-05-04 20:18 ` Paolo Bonzini
2021-05-04 19:55 ` Sean Christopherson
2021-05-04 20:26 ` Paolo Bonzini
2021-05-04 20:36 ` Sean Christopherson
2021-04-29 21:18 ` [PATCH v2 2/7] KVM: x86/mmu: Skip rmap operations if shadow MMU inactive Ben Gardon
2021-04-29 21:18 ` [PATCH v2 3/7] KVM: x86/mmu: Deduplicate rmap freeing Ben Gardon
2021-04-29 21:18 ` [PATCH v2 4/7] KVM: x86/mmu: Factor out allocating memslot rmap Ben Gardon
2021-04-29 21:18 ` [PATCH v2 5/7] KVM: mmu: Refactor memslot copy Ben Gardon
2021-04-29 21:18 ` [PATCH v2 6/7] KVM: mmu: Add slots_arch_lock for memslot arch fields Ben Gardon
2021-05-03 13:29 ` Paolo Bonzini
2021-04-29 21:18 ` [PATCH v2 7/7] KVM: x86/mmu: Lazily allocate memslot rmaps Ben Gardon
2021-05-03 13:42 ` Paolo Bonzini
2021-05-03 17:29 ` Ben Gardon
2021-05-04 20:13 ` Sean Christopherson
2021-05-04 20:19 ` Paolo Bonzini
2021-05-04 20:34 ` Sean Christopherson
2021-05-04 20:22 ` Paolo Bonzini
2021-05-03 13:44 ` Paolo Bonzini [this message]
2021-05-03 17:31 ` [PATCH v2 0/7] " Ben Gardon
2021-05-04 7:21 ` Paolo Bonzini
2021-05-04 17:28 ` Ben Gardon
2021-05-04 18:17 ` Sean Christopherson
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