The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 0910dd7c9ad45a2605c45fd2bf3d1bcac087687c # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025101348-gigahertz-cauterize-0303@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 0910dd7c9ad45a2605c45fd2bf3d1bcac087687c Mon Sep 17 00:00:00 2001 From: Sean Christopherson seanjc@google.com Date: Tue, 5 Aug 2025 12:05:09 -0700 Subject: [PATCH] KVM: SVM: Skip fastpath emulation on VM-Exit if next RIP isn't valid
Skip the WRMSR and HLT fastpaths in SVM's VM-Exit handler if the next RIP isn't valid, e.g. because KVM is running with nrips=false. SVM must decode and emulate to skip the instruction if the CPU doesn't provide the next RIP, and getting the instruction bytes to decode requires reading guest memory. Reading guest memory through the emulator can fault, i.e. can sleep, which is disallowed since the fastpath handlers run with IRQs disabled.
BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:106 in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 32611, name: qemu preempt_count: 1, expected: 0 INFO: lockdep is turned off. irq event stamp: 30580 hardirqs last enabled at (30579): [<ffffffffc08b2527>] vcpu_run+0x1787/0x1db0 [kvm] hardirqs last disabled at (30580): [<ffffffffb4f62e32>] __schedule+0x1e2/0xed0 softirqs last enabled at (30570): [<ffffffffb4247a64>] fpu_swap_kvm_fpstate+0x44/0x210 softirqs last disabled at (30568): [<ffffffffb4247a64>] fpu_swap_kvm_fpstate+0x44/0x210 CPU: 298 UID: 0 PID: 32611 Comm: qemu Tainted: G U 6.16.0-smp--e6c618b51cfe-sleep #782 NONE Tainted: [U]=USER Hardware name: Google Astoria-Turin/astoria, BIOS 0.20241223.2-0 01/17/2025 Call Trace: <TASK> dump_stack_lvl+0x7d/0xb0 __might_resched+0x271/0x290 __might_fault+0x28/0x80 kvm_vcpu_read_guest_page+0x8d/0xc0 [kvm] kvm_fetch_guest_virt+0x92/0xc0 [kvm] __do_insn_fetch_bytes+0xf3/0x1e0 [kvm] x86_decode_insn+0xd1/0x1010 [kvm] x86_emulate_instruction+0x105/0x810 [kvm] __svm_skip_emulated_instruction+0xc4/0x140 [kvm_amd] handle_fastpath_invd+0xc4/0x1a0 [kvm] vcpu_run+0x11a1/0x1db0 [kvm] kvm_arch_vcpu_ioctl_run+0x5cc/0x730 [kvm] kvm_vcpu_ioctl+0x578/0x6a0 [kvm] __se_sys_ioctl+0x6d/0xb0 do_syscall_64+0x8a/0x2c0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f479d57a94b </TASK>
Note, this is essentially a reapply of commit 5c30e8101e8d ("KVM: SVM: Skip WRMSR fastpath on VM-Exit if next RIP isn't valid"), but with different justification (KVM now grabs SRCU when skipping the instruction for other reasons).
Fixes: b439eb8ab578 ("Revert "KVM: SVM: Skip WRMSR fastpath on VM-Exit if next RIP isn't valid"") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20250805190526.1453366-2-seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index d9931c6c4bc6..829d9d46718d 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -4181,13 +4181,21 @@ static int svm_vcpu_pre_run(struct kvm_vcpu *vcpu) static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu) { struct vcpu_svm *svm = to_svm(vcpu); + struct vmcb_control_area *control = &svm->vmcb->control; + + /* + * Next RIP must be provided as IRQs are disabled, and accessing guest + * memory to decode the instruction might fault, i.e. might sleep. + */ + if (!nrips || !control->next_rip) + return EXIT_FASTPATH_NONE;
if (is_guest_mode(vcpu)) return EXIT_FASTPATH_NONE;
- switch (svm->vmcb->control.exit_code) { + switch (control->exit_code) { case SVM_EXIT_MSR: - if (!svm->vmcb->control.exit_info_1) + if (!control->exit_info_1) break; return handle_fastpath_set_msr_irqoff(vcpu); case SVM_EXIT_HLT: