From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f202.google.com (mail-pl1-f202.google.com [209.85.214.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1EABB3F787B for ; Fri, 29 May 2026 16:51:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780073489; cv=none; b=dtfEY34NgBnzBqrE89bScwtwmVX9gHz5EZY0Z+YssZiIbEp55EF3jNFaVpD0F+o8EnEtFl0W6na1g2PRHpoJEeMTtvE/uyY3NtcFVrd6+leFE2M0aPk29l8a/yy35+bWV894xU1DjNPlEK/Fwzujn2cA6jtpanKWdNh8iAav0XQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780073489; c=relaxed/simple; bh=WjoDBDihuoTsObsTRtzBi0FovEtka+bji/1FjjVQEiI=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=QlekwbXG0q+cN9RU6mhUnrHnmlxn/fawpBHID70iXzc2VYRRJJuMN/OyxmihJbGNNI09ijIkNNt8W5SA0NHX8T3tuiFE0loioc93y5DC5UsJA/Jco7TGEAr230jGdV+kNqqX8AzDpCffZXN2eMlhgMrh0HIPPm9GdJJrSJ+y8y4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=DniI1gUC; arc=none smtp.client-ip=209.85.214.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="DniI1gUC" Received: by mail-pl1-f202.google.com with SMTP id d9443c01a7336-2b4530a90fdso106708005ad.1 for ; Fri, 29 May 2026 09:51:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1780073485; x=1780678285; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:reply-to:from:to:cc:subject:date :message-id:reply-to; bh=fkSZAvSUuIZkLdKqbpwmfPEheEuKi4ON1NJkkf1RUcU=; b=DniI1gUCaOoqM1im4zrt2gs1XhJbyzYKvrnV86F/VNcEsBciIl+y0OBbZxdSJ0Dh23 HqEsuwXtZMNqRdoPfeTxy7DAjxVm9kmT/SbUhWMdLdjxJ+MZ90qPhKdyBqC+qS1RFaDZ 3VkU3pLkosyNZZL5IBApWX3V9CrqeVZtGkxGm3N0s4+DkzSUtVknC2UcrEHGAv/YSUZz Ob5Ww9ab8GtHTIWOlD6K/erDWFdbBF6bDhMCWr/bLvJkDVJrYTymWulyNCF5FH4JnKYv JAsz2QSQmnfDEZ4Eq2gmsetXrhZ12rznuinIuzTKq4Bo4EAtn2Ge+fXTaajJ3eGnOfSb FF4Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1780073485; x=1780678285; h=content-transfer-encoding:cc:to:from:subject:message-id:references :mime-version:in-reply-to:date:reply-to:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=fkSZAvSUuIZkLdKqbpwmfPEheEuKi4ON1NJkkf1RUcU=; b=E5Zf/2bFydwK5xdRqTLN4gGamBLnemNT91kX8z9xFfp5WDPMxM9joa5RTWDMPSQb+a h1Iyl1pfjV/PgVwunzX6h56Tr5kwVRiNMDA2hPENenRz4iINAismTb50QNhSvFhbDebh Lmx+Bfax5g1FmbT1AEujaBFlK8tc1+4xlMqN33FLJU34kkziTYMAaF6ctX6EiM6RYHSK 0mC3LuFGO+jPUPaUfPMqwn7iPXuuKw2jq03DDrvyFG6tBx3zrAbBmBd3VG1kwVHP+WA+ 7T2odDKPRAnQQ0aEaCVEtR3MHsLGLmS0OUPBdqBRXBR79ix8jBjG6xozaD4yJ+nWSyJE aJ9Q== X-Forwarded-Encrypted: i=1; AFNElJ+3v6kEQ762xAyZkVrb57/9mzj6dpyS+ZIuiLGpKgXR/ERI9A1sZx69cAPi0dekLo2/BsWHShI4EVBJUfA=@vger.kernel.org X-Gm-Message-State: AOJu0YxaPma+oOzFPLNe8ykJbmowkkP/mmQSlcbW+aUPGCJhEBkwDS+N 9gUfPMJCaKMTgdG28Pb7SMeMueDL1hqbAkjnV/aBd5mNk3GRjWv9VT9gg3DdrrvMbz6cBc5dya5 wgfyLZQ== X-Received: from pleu6.prod.google.com ([2002:a17:903:41c6:b0:2bf:1803:8eec]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:903:2f8d:b0:2b0:4fb6:85ce with SMTP id d9443c01a7336-2bf3684d836mr6960405ad.21.1780073485069; Fri, 29 May 2026 09:51:25 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 29 May 2026 09:50:56 -0700 In-Reply-To: <20260529165114.748639-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260529165114.748639-1-seanjc@google.com> X-Mailer: git-send-email 2.54.0.823.g6e5bcc1fc9-goog Message-ID: <20260529165114.748639-3-seanjc@google.com> Subject: [PATCH v2 02/20] KVM: x86/xen: Use read_trylock() for GPC locks in hardirq/atomic paths From: Sean Christopherson To: Sean Christopherson , Paolo Bonzini , David Woodhouse , Paul Durrant , Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng Cc: Waiman Long , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, David Woodhouse , Sebastian Andrzej Siewior , syzbot+208f7f3e5f59c11aeb90@syzkaller.appspotmail.com, Carsten Stollmaier Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable From: David Woodhouse kvm_xen_set_evtchn_fast() is called from hardirq context (timer callback, kvm_arch_set_irq_inatomic()). On PREEMPT_RT, rwlock_t is a sleeping lock, so read_lock_irqsave() cannot be used in this context. Switch to read_trylock() and return -EWOULDBLOCK on contention, which is the designed fallback =E2=80=94 there is always a slow path for the case wh= ere the GPC is invalid and needs to be refreshed. Reported-by: syzbot+208f7f3e5f59c11aeb90@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D208f7f3e5f59c11aeb90 Fixes: 14243b387137 ("KVM: x86/xen: Add KVM_IRQ_ROUTING_XEN_EVTCHN and even= t channel delivery") Signed-off-by: David Woodhouse Signed-off-by: Sean Christopherson --- arch/x86/kvm/xen.c | 32 +++++++++++++++++++++++--------- 1 file changed, 23 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index 91fd3673c09a..9bdb8e3cad58 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -697,6 +697,7 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v) int __kvm_xen_has_interrupt(struct kvm_vcpu *v) { struct gfn_to_pfn_cache *gpc =3D &v->arch.xen.vcpu_info_cache; + bool atomic =3D in_atomic() || !task_is_running(current); unsigned long flags; u8 rc =3D 0; =20 @@ -713,7 +714,15 @@ int __kvm_xen_has_interrupt(struct kvm_vcpu *v) BUILD_BUG_ON(sizeof(rc) !=3D sizeof_field(struct compat_vcpu_info, evtchn_upcall_pending)); =20 - read_lock_irqsave(&gpc->lock, flags); + if (atomic) { + local_irq_save(flags); + if (!read_trylock(&gpc->lock)) { + local_irq_restore(flags); + return 1; + } + } else { + read_lock_irqsave(&gpc->lock, flags); + } while (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) { read_unlock_irqrestore(&gpc->lock, flags); =20 @@ -725,7 +734,7 @@ int __kvm_xen_has_interrupt(struct kvm_vcpu *v) * and we'll end up getting called again from a context where we *can* * fault in the page and wait for it. */ - if (in_atomic() || !task_is_running(current)) + if (atomic) return 1; =20 if (kvm_gpc_refresh(gpc, sizeof(struct vcpu_info))) { @@ -1794,7 +1803,6 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe= , struct kvm *kvm) struct gfn_to_pfn_cache *gpc =3D &kvm->arch.xen.shinfo_cache; struct kvm_vcpu *vcpu; unsigned long *pending_bits, *mask_bits; - unsigned long flags; int port_word_bit; bool kick_vcpu =3D false; int vcpu_idx, idx, rc; @@ -1816,9 +1824,10 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *x= e, struct kvm *kvm) =20 idx =3D srcu_read_lock(&kvm->srcu); =20 - read_lock_irqsave(&gpc->lock, flags); - if (!kvm_gpc_check(gpc, PAGE_SIZE)) + if (!read_trylock(&gpc->lock)) goto out_rcu; + if (!kvm_gpc_check(gpc, PAGE_SIZE)) + goto out_unlock; =20 if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) { struct shared_info *shinfo =3D gpc->khva; @@ -1847,11 +1856,10 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *= xe, struct kvm *kvm) } else { rc =3D 1; /* Delivered to the bitmap in shared_info. */ /* Now switch to the vCPU's vcpu_info to set the index and pending_sel *= / - read_unlock_irqrestore(&gpc->lock, flags); + read_unlock(&gpc->lock); gpc =3D &vcpu->arch.xen.vcpu_info_cache; =20 - read_lock_irqsave(&gpc->lock, flags); - if (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) { + if (!read_trylock(&gpc->lock)) { /* * Could not access the vcpu_info. Set the bit in-kernel * and prod the vCPU to deliver it for itself. @@ -1860,6 +1868,11 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *x= e, struct kvm *kvm) kick_vcpu =3D true; goto out_rcu; } + if (!kvm_gpc_check(gpc, sizeof(struct vcpu_info))) { + if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel= )) + kick_vcpu =3D true; + goto out_unlock; + } =20 if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) { struct vcpu_info *vcpu_info =3D gpc->khva; @@ -1883,8 +1896,9 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe= , struct kvm *kvm) } } =20 + out_unlock: + read_unlock(&gpc->lock); out_rcu: - read_unlock_irqrestore(&gpc->lock, flags); srcu_read_unlock(&kvm->srcu, idx); =20 if (kick_vcpu) { --=20 2.54.0.823.g6e5bcc1fc9-goog