On Fri, Feb 23, 2024 at 10:15 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > Two more MMU-related fixes for 6.8. The first, and worst, fixes a data > corruption bug during live migration due to KVM failing to mark a memslot > dirty when emulating an atomic access. Luckily, our userspace caught the > corruption during checksumming after the final pause, but I've no idea if > QEMU-based VMs have such protection. > > The second fixes a long-standing, but recently exposed, issue where yielding > mmu_lock to vCPUs attempting to fault in memory that is _currently_ being > zapped/modified can bog down the invalidation task due it constantly yielding > to vCPUS (which end up doing nothing). > > The following changes since commit 9895ceeb5cd61092f147f8d611e2df575879dd6f: > > Merge tag 'kvmarm-fixes-6.8-2' of git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD (2024-02-16 12:02:38 -0500) > > are available in the Git repository at: > > https://github.com/kvm-x86/linux.git tags/kvm-x86-fixes-6.8-2 > > for you to fetch changes up to d02c357e5bfa7dfd618b7b3015624beb71f58f1f: > > KVM: x86/mmu: Retry fault before acquiring mmu_lock if mapping is changing (2024-02-23 10:14:34 -0800) Pulled, thanks. Paolo > ---------------------------------------------------------------- > KVM x86 fixes for 6.8, round 2: > > - When emulating an atomic access, mark the gfn as dirty in the memslot > to fix a bug where KVM could fail to mark the slot as dirty during live > migration, ultimately resulting in guest data corruption due to a dirty > page not being re-copied from the source to the target. > > - Check for mmu_notifier invalidation events before faulting in the pfn, > and before acquiring mmu_lock, to avoid unnecessary work and lock > contention. Contending mmu_lock is especially problematic on preemptible > kernels, as KVM may yield mmu_lock in response to the contention, which > severely degrades overall performance due to vCPUs making it difficult > for the task that triggered invalidation to make forward progress. > > Note, due to another kernel bug, this fix isn't limited to preemtible > kernels, as any kernel built with CONFIG_PREEMPT_DYNAMIC=y will yield > contended rwlocks and spinlocks. > > https://lore.kernel.org/all/20240110214723.695930-1-seanjc@xxxxxxxxxx > > ---------------------------------------------------------------- > Sean Christopherson (2): > KVM: x86: Mark target gfn of emulated atomic instruction as dirty > KVM: x86/mmu: Retry fault before acquiring mmu_lock if mapping is changing > > arch/x86/kvm/mmu/mmu.c | 42 ++++++++++++++++++++++++++++++++++++++++++ > arch/x86/kvm/x86.c | 10 ++++++++++ > include/linux/kvm_host.h | 26 ++++++++++++++++++++++++++ > 3 files changed, 78 insertions(+) >
