https://bugzilla.kernel.org/show_bug.cgi?id=219588 --- Comment #5 from leiyang@xxxxxxxxxx --- Due to the fixed patch has been merge into the upstream master branch, so close done this bug. commit 386d69f9f29b0814881fa4f92ac7b8dfa9b4f44a Author: Sean Christopherson <seanjc@xxxxxxxxxx> Date: Wed Dec 18 13:36:11 2024 -0800 KVM: x86/mmu: Treat TDP MMU faults as spurious if access is already allowed Treat slow-path TDP MMU faults as spurious if the access is allowed given the existing SPTE to fix a benign warning (other than the WARN itself) due to replacing a writable SPTE with a read-only SPTE, and to avoid the unnecessary LOCK CMPXCHG and subsequent TLB flush. If a read fault races with a write fault, fast GUP fails for any reason when trying to "promote" the read fault to a writable mapping, and KVM resolves the write fault first, then KVM will end up trying to install a read-only SPTE (for a !map_writable fault) overtop a writable SPTE. Note, it's not entirely clear why fast GUP fails, or if that's even how KVM ends up with a !map_writable fault with a writable SPTE. If something else is going awry, e.g. due to a bug in mmu_notifiers, then treating read faults as spurious in this scenario could effectively mask the underlying problem. However, retrying the faulting access instead of overwriting an existing SPTE is functionally correct and desirable irrespective of the WARN, and fast GUP _can_ legitimately fail with a writable VMA, e.g. if the Accessed bit in primary MMU's PTE is toggled and causes a PTE value mismatch. The WARN was also recently added, specifically to track down scenarios where KVM is unnecessarily overwrites SPTEs, i.e. treating the fault as spurious doesn't regress KVM's bug-finding capabilities in any way. In short, letting the WARN linger because there's a tiny chance it's due to a bug elsewhere would be excessively paranoid. Fixes: 1a175082b190 ("KVM: x86/mmu: WARN and flush if resolving a TDP MMU fault clears MMU-writable") Reported-by: Lei Yang <leiyang@xxxxxxxxxx> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219588 -- You may reply to this email to add a comment. You are receiving this mail because: You are watching the assignee of the bug.
