From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 66452CA0FF6 for ; Thu, 28 Aug 2025 23:56:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=za39H7FcroRUdOegM69guGFyGLSm+e+5RxybRN7+0As=; b=mA6YNLRvjYVNXo fzNmovpxlP2IMiTTB8lTbEmvV1jm5rdkbqRjc+TwfAsDUx21OTUByEzDBtvPdPOCQTUvUBnekFKMn g65tvOu2mf8Jkoylct962A1UhcQLE86S+RWDi9de8MXrPOqHb4i4CZIMo750yXiaJm67qIieOrUvP gW1+V0HBugYdVechi6zumhJNJWYWcBL0HEKuRDiIXYaGHq/JOSuyNE6bTHc/KzFIhhNzf4q+BZcRZ sgnESjghfvRHuxA26anKbX1GttML+fI5wmyOO528IpCNBtnT9CslrDngWiUxqviTl5NZl+yZiw2qw gRkg8l4tHACXP7a4768g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1urmTr-00000003k4R-3gJc; Thu, 28 Aug 2025 23:56:35 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1urmTq-00000003k3t-0XJC; Thu, 28 Aug 2025 23:56:35 +0000 Received: from [100.65.128.219] (unknown [20.236.11.69]) by linux.microsoft.com (Postfix) with ESMTPSA id 6157F2110814; Thu, 28 Aug 2025 16:56:31 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 6157F2110814 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1756425392; bh=pCexqDkoW83y7LpImpFx62Xw3cNxneYeXhAEgKffuKE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=FCmBOZwwR8w+zLgYvdYsQndKdjVa/Zic9g+xriRNGxIyvlCW/6jpNTSZnJfm6AeYV w2ojPM1lFjNBJBy+LYvZF2V3PzDSbQwMQWAu7ekzKLIlFXUd3JJs7xNFRWV7yBhSjO k2ChjjpZ1AKeJCgw2XX5B7Ss1Fvkq4e5nLRu23ks= Message-ID: <0b4eb0cc-657f-4cdb-8255-e3b8f6b14077@linux.microsoft.com> Date: Thu, 28 Aug 2025 16:56:20 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/7] Drivers: hv: Handle NEED_RESCHED_LAZY before transferring to guest To: Sean Christopherson , Marc Zyngier , Oliver Upton , Catalin Marinas , Will Deacon , Tianrui Zhao , Bibo Mao , Huacai Chen , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Peter Zijlstra , Andy Lutomirski , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Uladzislau Rezki Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, loongarch@lists.linux.dev, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-hyperv@vger.kernel.org, rcu@vger.kernel.org, Mukesh R References: <20250828000156.23389-1-seanjc@google.com> <20250828000156.23389-2-seanjc@google.com> Content-Language: en-US From: Nuno Das Neves In-Reply-To: <20250828000156.23389-2-seanjc@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250828_165634_226782_853EAD5E X-CRM114-Status: GOOD ( 17.09 ) X-BeenThere: kvm-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kvm-riscv" Errors-To: kvm-riscv-bounces+kvm-riscv=archiver.kernel.org@lists.infradead.org On 8/27/2025 5:01 PM, Sean Christopherson wrote: > Check for NEED_RESCHED_LAZY, not just NEED_RESCHED, prior to transferring > control to a guest. Failure to check for lazy resched can unnecessarily > delay rescheduling until the next tick when using a lazy preemption model. > > Note, ideally both the checking and processing of TIF bits would be handled > in common code, to avoid having to keep three separate paths synchronized, > but defer such cleanups to the future to keep the fix as standalone as > possible. > > Cc: Nuno Das Neves > Cc: Mukesh R > Fixes: 621191d709b1 ("Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs") > Fixes: 64503b4f4468 ("Drivers: hv: Introduce mshv_vtl driver") > Signed-off-by: Sean Christopherson > --- > drivers/hv/mshv_common.c | 2 +- > drivers/hv/mshv_root_main.c | 3 ++- > drivers/hv/mshv_vtl_main.c | 3 ++- > 3 files changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/hv/mshv_common.c b/drivers/hv/mshv_common.c > index 6f227a8a5af7..eb3df3e296bb 100644 > --- a/drivers/hv/mshv_common.c > +++ b/drivers/hv/mshv_common.c > @@ -151,7 +151,7 @@ int mshv_do_pre_guest_mode_work(ulong th_flags) > if (th_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL)) > return -EINTR; > > - if (th_flags & _TIF_NEED_RESCHED) > + if (th_flags & (_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY)) > schedule(); > > if (th_flags & _TIF_NOTIFY_RESUME) > diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c > index 932932cb91ea..0d849f09160a 100644 > --- a/drivers/hv/mshv_root_main.c > +++ b/drivers/hv/mshv_root_main.c > @@ -484,7 +484,8 @@ mshv_vp_wait_for_hv_kick(struct mshv_vp *vp) > static int mshv_pre_guest_mode_work(struct mshv_vp *vp) > { > const ulong work_flags = _TIF_NOTIFY_SIGNAL | _TIF_SIGPENDING | > - _TIF_NEED_RESCHED | _TIF_NOTIFY_RESUME; > + _TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY | > + _TIF_NOTIFY_RESUME; > ulong th_flags; > > th_flags = read_thread_flags(); > diff --git a/drivers/hv/mshv_vtl_main.c b/drivers/hv/mshv_vtl_main.c > index dc6594ae03ad..12f5e77b7095 100644 > --- a/drivers/hv/mshv_vtl_main.c > +++ b/drivers/hv/mshv_vtl_main.c > @@ -728,7 +728,8 @@ static int mshv_vtl_ioctl_return_to_lower_vtl(void) > preempt_disable(); > for (;;) { > const unsigned long VTL0_WORK = _TIF_SIGPENDING | _TIF_NEED_RESCHED | > - _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL; > + _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL | > + _TIF_NEED_RESCHED_LAZY; > unsigned long ti_work; > u32 cancel; > unsigned long irq_flags; Tested by compiling with CONFIG_PREEMPT_LAZY=y and booting a guest. For the test I added a check to confirm _TIF_NEED_RESCHED_LAZY was set and honored. Looks good, thanks. Tested-by: Nuno Das Neves Reviewed-by: Nuno Das Neves -- kvm-riscv mailing list kvm-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kvm-riscv