linux-kernel - [PATCH v2 0/5] KVM: Dirty ring fixes and cleanups

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Message-ID: <20250508141012.1411952-1-seanjc@google.com>
Date: Thu,  8 May 2025 07:10:07 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Peter Xu <peterx@...hat.com>, Yan Zhao <yan.y.zhao@...el.com>, 
	Maxim Levitsky <mlevitsk@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH v2 0/5] KVM: Dirty ring fixes and cleanups

Fix issues with dirty ring harvesting where KVM doesn't bound the processing
of entries in any way, which allows userspace to keep KVM in a tight loop
indefinitely.

E.g.

        struct kvm_dirty_gfn *dirty_gfns = vcpu_map_dirty_ring(vcpu);

        if (fork()) {
                int r;

                for (;;) {
                        r = kvm_vm_reset_dirty_ring(vcpu->vm);
                        if (r)
                                printf("RESET %d dirty ring entries\n", r);
                }
        } else {
                int i;

                for (i = 0; i < test_dirty_ring_count; i++) {
                        dirty_gfns[i].slot = TEST_MEM_SLOT_INDEX;
                        dirty_gfns[i].offset = (i * 64) % host_num_pages;
                }

                for (;;) {
                        for (i = 0; i < test_dirty_ring_count; i++)
                                WRITE_ONCE(dirty_gfns[i].flags, KVM_DIRTY_GFN_F_RESET);
                }
        }

Patches 1-3 address that class of bugs.  Patches 4 and 5 are cleanups.


v2: Expand on comments in dirty ring harvesting code. [Yan]

v1: https://lore.kernel.org/all/20250111010409.1252942-1-seanjc@google.com

Sean Christopherson (5):
  KVM: Bound the number of dirty ring entries in a single reset at
    INT_MAX
  KVM: Bail from the dirty ring reset flow if a signal is pending
  KVM: Conditionally reschedule when resetting the dirty ring
  KVM: Check for empty mask of harvested dirty ring entries in caller
  KVM: Use mask of harvested dirty ring entries to coalesce dirty ring
    resets

 include/linux/kvm_dirty_ring.h |   8 ++-
 virt/kvm/dirty_ring.c          | 103 ++++++++++++++++++++++-----------
 virt/kvm/kvm_main.c            |   9 ++-
 3 files changed, 81 insertions(+), 39 deletions(-)


base-commit: d1b88431c59e94799aff0e31ce1467af2a86b0cf
-- 
2.49.0.1015.ga840276032-goog