diff options
| author | Sean Christopherson <seanjc@google.com> | 2026-01-08 19:06:57 -0800 |
|---|---|---|
| committer | Sasha Levin <sashal@kernel.org> | 2026-03-12 07:09:27 -0400 |
| commit | 1e88b5f854bdb469424132e0bb44793ad7a7c20a (patch) | |
| tree | 74151f6b601f9c04e4627b3ab13a5e9bb2c9f86a /arch/x86 | |
| parent | 2dff8966a3a889dd9d248a7e15d963b4097efcc5 (diff) | |
KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()
[ Upstream commit ead63640d4e72e6f6d464f4e31f7fecb79af8869 ]
Ignore -EBUSY when checking nested events after exiting a blocking state
while L2 is active, as exiting to userspace will generate a spurious
userspace exit, usually with KVM_EXIT_UNKNOWN, and likely lead to the VM's
demise. Continuing with the wakeup isn't perfect either, as *something*
has gone sideways if a vCPU is awakened in L2 with an injected event (or
worse, a nested run pending), but continuing on gives the VM a decent
chance of surviving without any major side effects.
As explained in the Fixes commits, it _should_ be impossible for a vCPU to
be put into a blocking state with an already-injected event (exception,
IRQ, or NMI). Unfortunately, userspace can stuff MP_STATE and/or injected
events, and thus put the vCPU into what should be an impossible state.
Don't bother trying to preserve the WARN, e.g. with an anti-syzkaller
Kconfig, as WARNs can (hopefully) be added in paths where _KVM_ would be
violating x86 architecture, e.g. by WARNing if KVM attempts to inject an
exception or interrupt while the vCPU isn't running.
Cc: Alessandro Ratti <alessandro@0x65c.net>
Cc: stable@vger.kernel.org
Fixes: 26844fee6ade ("KVM: x86: never write to memory from kvm_vcpu_check_block()")
Fixes: 45405155d876 ("KVM: x86: WARN if a vCPU gets a valid wakeup that KVM can't yet inject")
Link: https://syzkaller.appspot.com/text?tag=ReproC&x=10d4261a580000
Reported-by: syzbot+1522459a74d26b0ac33a@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/671bc7a7.050a0220.455e8.022a.GAE@google.com
Link: https://patch.msgid.link/20260109030657.994759-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/kvm/x86.c | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index aeb7f902b3c7..2ab445c0126b 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11598,8 +11598,7 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu) if (is_guest_mode(vcpu)) { int r = kvm_check_nested_events(vcpu); - WARN_ON_ONCE(r == -EBUSY); - if (r < 0) + if (r < 0 && r != -EBUSY) return 0; } |