From patchwork Tue Feb 27 11:49:21 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: David Woodhouse X-Patchwork-Id: 13573625 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 5253E12F581 for ; Tue, 27 Feb 2024 11:56:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709035019; cv=none; b=KDQ7uyk1CavrvKdlFMQ9lajdUI4FnUm1OA1iZseIPe27i7rpsMKtix23t+1y3rTd1tr/WYIZo6DhXImGsMdCJB46RzHT2vqP2yBFhUM/KmbhYKg/W1nEzVTP3cn2mxbP+zrYZ5njzN63Q8gQKEcBpR9HJdnulN1tZLEePBGzH+I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1709035019; c=relaxed/simple; bh=HnO4xc35jrQguliZlaxh0Zjk4Ght5IMc72SPKCT//yU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ZJBLPwNQA0dq3AvLWw2mpA1Hn+gN2UXNwUGWJtnxp29kCX/xHQCQWH1SJZIVzm2WIm9rk//8Uj3oA7VRTUJtVONMhHKSZCCN0A/bnfcw3Jesd/jzquOGhurUhIj+ddMw+Y7lzNh5UdfQ9jI2scLMDMkFSSwtErHLFOzLogrSdlc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=YxmnW8DC; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="YxmnW8DC" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=Sender:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc: To:From:Reply-To:Content-ID:Content-Description; bh=HJUVfEzfpfQ6/ZOZU2Or4QVmUenWrNRUEquSgFacOeg=; b=YxmnW8DCXiTyZ8pcRLtCqNUsNx NGPlnjajQOQTeJCGu/ga+g2cxs0ynH0FryA2aV4sJSBemM/0Eliehqn+NCfp/0np2CY4g2fpPXqzQ c014A5XvrCvtW6acDeDDsTyMiuW3xHhA1GS6nQ2rL3OZD23aXdxgD1I+AzWenz4d8rM7H3c+8ezVm WbfdlbTwVx74kEMlqafW3RVBg3NpZX9CeBpmsHyhh3q7kri0E8FWaruLJUO5xJPOKf06IZwvMMnF1 Kw3gYUBSVdYH+k+maWwaiPT8MZ3tdGuZMb7b2Vh1Cxkt4xVYJLKfsmjop/IWYyUFuYrSrjrt1lgF1 izTCsDIw==; Received: from [2001:8b0:10b:1::ebe] (helo=i7.infradead.org) by desiato.infradead.org with esmtpsa (Exim 4.97.1 #2 (Red Hat Linux)) id 1rew4p-00000001j63-3s5b; Tue, 27 Feb 2024 11:56:52 +0000 Received: from dwoodhou by i7.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1rew4o-000000000wh-0W6o; Tue, 27 Feb 2024 11:56:50 +0000 From: David Woodhouse To: kvm@vger.kernel.org Cc: Sean Christopherson , Paul Durrant , Paolo Bonzini , Michal Luczaj , Paul Durrant , David Woodhouse , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Peter Zijlstra , Steven Rostedt , Dave Hansen , "H. Peter Anvin" , David Woodhouse , x86@kernel.org Subject: [PATCH v2 7/8] KVM: x86/xen: avoid blocking in hardirq context in kvm_xen_set_evtchn_fast() Date: Tue, 27 Feb 2024 11:49:21 +0000 Message-ID: <20240227115648.3104-8-dwmw2@infradead.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240227115648.3104-1-dwmw2@infradead.org> References: <20240227115648.3104-1-dwmw2@infradead.org> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Sender: David Woodhouse X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html From: Paul Durrant As described in [1] compiling with CONFIG_PROVE_RAW_LOCK_NESTING shows that kvm_xen_set_evtchn_fast() is blocking on pfncache locks in IRQ context. There is only actually blocking with PREEMPT_RT because the locks will turned into mutexes. There is no 'raw' version of rwlock_t that can be used to avoid that, so use read_trylock() and treat failure to lock the same as an invalid cache. [1] https://lore.kernel.org/lkml/99771ef3a4966a01fefd3adbb2ba9c3a75f97cf2.camel@infradead.org/T/#mbd06e5a04534ce9c0ee94bd8f1e8d942b2d45bd6 Fixes: 77c9b9dea4fb ("KVM: x86/xen: Use fast path for Xen timer delivery") Signed-off-by: Paul Durrant Reviewed-by: David Woodhouse Signed-off-by: Paul Durrant Signed-off-by: David Woodhouse --- Cc: Sean Christopherson Cc: Paolo Bonzini Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Dave Hansen Cc: "H. Peter Anvin" Cc: David Woodhouse Cc: x86@kernel.org v2: • Use read_trylock only in interrupt context, to avoid concerns about unfairness in the slow path. --- arch/x86/kvm/xen.c | 41 +++++++++++++++++++++++++++++++---------- 1 file changed, 31 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c index c16b6d394d55..d8b5326ecebc 100644 --- a/arch/x86/kvm/xen.c +++ b/arch/x86/kvm/xen.c @@ -1736,9 +1736,23 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) unsigned long flags; int rc = -EWOULDBLOCK; - read_lock_irqsave(&gpc->lock, flags); + local_irq_save(flags); + if (!read_trylock(&gpc->lock)) { + /* + * When PREEMPT_RT turns locks into mutexes, rwlocks are + * turned into mutexes and most interrupts are threaded. + * But timer events may be delivered in hardirq mode due + * to using HRTIMER_MODE_ABS_HARD. So bail to the slow + * path if the trylock fails in interrupt context. + */ + if (in_interrupt()) + goto out; + + read_lock(&gpc->lock); + } + if (!kvm_gpc_check(gpc, PAGE_SIZE)) - goto out; + goto out_unlock; if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) { struct shared_info *shinfo = gpc->khva; @@ -1761,8 +1775,10 @@ static int set_shinfo_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) rc = 1; /* It is newly raised */ } + out_unlock: + read_unlock(&gpc->lock); out: - read_unlock_irqrestore(&gpc->lock, flags); + local_irq_restore(flags); return rc; } @@ -1772,21 +1788,23 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) struct gfn_to_pfn_cache *gpc = &vcpu->arch.xen.vcpu_info_cache; unsigned long flags; bool kick_vcpu = false; + bool locked; - read_lock_irqsave(&gpc->lock, flags); + local_irq_save(flags); + locked = read_trylock(&gpc->lock); /* * Try to deliver the event directly to the vcpu_info. If successful and * the guest is using upcall_vector delivery, send the MSI. - * If the pfncache is invalid, set the shadow. In this case, or if the - * guest is using another form of event delivery, the vCPU must be - * kicked to complete the delivery. + * If the pfncache lock is contended or the cache is invalid, set the + * shadow. In this case, or if the guest is using another form of event + * delivery, the vCPU must be kicked to complete the delivery. */ if (IS_ENABLED(CONFIG_64BIT) && kvm->arch.xen.long_mode) { struct vcpu_info *vcpu_info = gpc->khva; int port_word_bit = port / 64; - if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) { + if ((!locked || !kvm_gpc_check(gpc, sizeof(*vcpu_info)))) { if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel)) kick_vcpu = true; goto out; @@ -1800,7 +1818,7 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) struct compat_vcpu_info *vcpu_info = gpc->khva; int port_word_bit = port / 32; - if (!kvm_gpc_check(gpc, sizeof(*vcpu_info))) { + if ((!locked || !kvm_gpc_check(gpc, sizeof(*vcpu_info)))) { if (!test_and_set_bit(port_word_bit, &vcpu->arch.xen.evtchn_pending_sel)) kick_vcpu = true; goto out; @@ -1819,7 +1837,10 @@ static bool set_vcpu_info_evtchn_pending(struct kvm_vcpu *vcpu, u32 port) } out: - read_unlock_irqrestore(&gpc->lock, flags); + if (locked) + read_unlock(&gpc->lock); + + local_irq_restore(flags); return kick_vcpu; }