From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6ADD221CC58; Sun, 1 Mar 2026 01:15:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772327734; cv=none; b=ZWqkI2yRnyXTQRu4CtcfupkdqAtF/eqYYgl+tLPgj22VNO+2X3FHy4cA0kIcW0TeCbJH/3nTxdsFk5T3oS9UhAsC+HWMk0oEF1tDWLj+ixlZQ9Cu2GlrMSMfhJd8R4PzwU1IZ0RbfFTxAoACDT+SdpktY1/rXaFq/gqP8p3a7cU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772327734; c=relaxed/simple; bh=q1KzisR7YydyGnrLR8TJKjUW4vGofbE3oDGsOOqxC24=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=GtMVfWd+PJ15VwP/+E9izrffvkH1M4KXbH7OAxkLVPYA3+YaZKzuSADmJkec6KkapadO1f2wK7y6k9hKXx3cGpra+mVqelWANaiKvhBnlqUIJ/tVQyjvOMbyGCP2hn6dfFx1VWgHvnLhfKBhM8K9aZcHrTPBx80+NQw2WsSN6uw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AfPaOegL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AfPaOegL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BDC32C19421; Sun, 1 Mar 2026 01:15:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772327734; bh=q1KzisR7YydyGnrLR8TJKjUW4vGofbE3oDGsOOqxC24=; h=From:To:Cc:Subject:Date:From; b=AfPaOegLBOFU+hWGVTA7HntqYQKei6+f1zh4tqKTPTvWjVHwmTLbDD+zS9DAJCH82 LyOtR1Bjg6E3iVPJg1LtLVW5wMLctcoQexT2Tdy+i4Gnu5SM6rQ/klGjkuVI3E/5Tp UQ8zYhVbaJpAtqbxcYSKIc3ln3BpD5xycVFUScTJD20VKyk0sA4OTkypGO0JjSzEoI dBtVql6y/OsENTIhRmlkThRb803IRJLxydPVbGcZmJqfCqFqB+8WpG4jGtsAW0/ag9 SVthhZhIpKoMWBA2fPx3huqS17GIMd/VjHHEW2KjqRt5+I3V8a6Xsb4hnNBeEHZA2y xLMM4jnJa7dmA== From: Sasha Levin To: stable@vger.kernel.org, seanjc@google.com Cc: Alessandro Ratti , syzbot+1522459a74d26b0ac33a@syzkaller.appspotmail.com, kvm@vger.kernel.org Subject: FAILED: Patch "KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()" failed to apply to 6.18-stable tree Date: Sat, 28 Feb 2026 20:15:32 -0500 Message-ID: <20260301011532.1668942-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Hint: ignore X-stable: review Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.18-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 . Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From ead63640d4e72e6f6d464f4e31f7fecb79af8869 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 8 Jan 2026 19:06:57 -0800 Subject: [PATCH] KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block() 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 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 --- arch/x86/kvm/x86.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index e4418409b468d..fe9d324da72ab 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11597,8 +11597,7 @@ 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; } -- 2.51.0