From patchwork Tue Dec 19 16:11:08 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Durrant X-Patchwork-Id: 756280 Received: from mail.xenproject.org (mail.xenproject.org [104.130.215.37]) (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 4731A358AB; Tue, 19 Dec 2023 16:41:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=xen.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=xen.org header.i=@xen.org header.b="p+0hw2zs" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:MIME-Version:References: In-Reply-To:Message-Id:Date:Subject:To:From; bh=z7zH+v6OnxjwAjiPJoCCBsbBFCz5/p3/vhyVHwUde2s=; b=p+0hw2zsYJOzIGTveKGHhHTwG3 +fuOn7o4duxP5GOylzP/2h4eiWIGHrlQIr2s0s/tF7In22LN7qFw+yvrera/lZGJkRR6BByhU+d4y 9MCpDA+p7j1WuD2SwFFPRIHwEiX+wEuiWftpnJWOG0mJxl54FO4ziy5iQXCDrLqZNw9s=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1rFd9y-000657-BU; Tue, 19 Dec 2023 16:41:34 +0000 Received: from 54-240-197-226.amazon.com ([54.240.197.226] helo=REM-PW02S00X.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1rFckR-0005h9-QH; Tue, 19 Dec 2023 16:15:12 +0000 From: Paul Durrant To: Paolo Bonzini , Jonathan Corbet , Sean Christopherson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , David Woodhouse , Paul Durrant , Shuah Khan , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v11 18/19] KVM: pfncache: check the need for invalidation under read lock first Date: Tue, 19 Dec 2023 16:11:08 +0000 Message-Id: <20231219161109.1318-19-paul@xen.org> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20231219161109.1318-1-paul@xen.org> References: <20231219161109.1318-1-paul@xen.org> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Paul Durrant Taking a write lock on a pfncache will be disruptive if the cache is heavily used (which only requires a read lock). Hence, in the MMU notifier callback, take read locks on caches to check for a match; only taking a write lock to actually perform an invalidation (after a another check). Signed-off-by: Paul Durrant Reviewed-by: David Woodhouse --- Cc: Sean Christopherson Cc: Paolo Bonzini Cc: David Woodhouse v10: - New in this version. --- virt/kvm/pfncache.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c index ae822bff812f..70394d7c9a38 100644 --- a/virt/kvm/pfncache.c +++ b/virt/kvm/pfncache.c @@ -29,14 +29,30 @@ void gfn_to_pfn_cache_invalidate_start(struct kvm *kvm, unsigned long start, spin_lock(&kvm->gpc_lock); list_for_each_entry(gpc, &kvm->gpc_list, list) { - write_lock_irq(&gpc->lock); + read_lock_irq(&gpc->lock); /* Only a single page so no need to care about length */ if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) && gpc->uhva >= start && gpc->uhva < end) { - gpc->valid = false; + read_unlock_irq(&gpc->lock); + + /* + * There is a small window here where the cache could + * be modified, and invalidation would no longer be + * necessary. Hence check again whether invalidation + * is still necessary once the write lock has been + * acquired. + */ + + write_lock_irq(&gpc->lock); + if (gpc->valid && !is_error_noslot_pfn(gpc->pfn) && + gpc->uhva >= start && gpc->uhva < end) + gpc->valid = false; + write_unlock_irq(&gpc->lock); + continue; } - write_unlock_irq(&gpc->lock); + + read_unlock_irq(&gpc->lock); } spin_unlock(&kvm->gpc_lock); }