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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B9B1C25B78 for ; Wed, 22 May 2024 15:26:36 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=MR8HfGt/; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4Vkw0S06fjz78gh for ; Thu, 23 May 2024 01:17:44 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=MR8HfGt/; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.dev (client-ip=95.215.58.175; helo=out-175.mta1.migadu.com; envelope-from=oliver.upton@linux.dev; receiver=lists.ozlabs.org) Received: from out-175.mta1.migadu.com (out-175.mta1.migadu.com [95.215.58.175]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4VkvzZ3M4kz3g8v for ; Thu, 23 May 2024 01:16:58 +1000 (AEST) X-Envelope-To: seanjc@google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1716390977; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=qPx5VBeAtVusPub5h8jjoS2Zp/k7LiSDo3T23EUz3Cc=; b=MR8HfGt/7NWj1OeZKFuwxnVF9+ndS7xCoaOY+r1JI2bWBzf2MynLiEMDjC1DrcozAH8hei TUnFiYL5Pyj+E10/+shwWi4h/9LVvu0Mc6mkr1yRH6n++3msAFiuDQVzo86zkrGkaVb0hH 6NbyKC1AGLafKPP8z0hv7d6a9IuqBaQ= X-Envelope-To: maz@kernel.org X-Envelope-To: zhaotianrui@loongson.cn X-Envelope-To: maobibo@loongson.cn X-Envelope-To: chenhuacai@kernel.org X-Envelope-To: mpe@ellerman.id.au X-Envelope-To: anup@brainfault.org X-Envelope-To: paul.walmsley@sifive.com X-Envelope-To: palmer@dabbelt.com X-Envelope-To: aou@eecs.berkeley.edu X-Envelope-To: borntraeger@linux.ibm.com X-Envelope-To: frankja@linux.ibm.com X-Envelope-To: imbrenda@linux.ibm.com X-Envelope-To: pbonzini@redhat.com X-Envelope-To: linux-arm-kernel@lists.infradead.org X-Envelope-To: kvmarm@lists.linux.dev X-Envelope-To: kvm@vger.kernel.org X-Envelope-To: loongarch@lists.linux.dev X-Envelope-To: linux-mips@vger.kernel.org X-Envelope-To: linuxppc-dev@lists.ozlabs.org X-Envelope-To: kvm-riscv@lists.infradead.org X-Envelope-To: linux-riscv@lists.infradead.org X-Envelope-To: linux-kernel@vger.kernel.org Date: Wed, 22 May 2024 08:16:07 -0700 X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Oliver Upton To: Sean Christopherson Subject: Re: [PATCH v2 1/6] KVM: Add a flag to track if a loaded vCPU is scheduled out Message-ID: References: <20240522014013.1672962-1-seanjc@google.com> <20240522014013.1672962-2-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240522014013.1672962-2-seanjc@google.com> X-Migadu-Flow: FLOW_OUT X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Claudio Imbrenda , Janosch Frank , Marc Zyngier , Huacai Chen , Christian Borntraeger , Albert Ou , Bibo Mao , loongarch@lists.linux.dev, Paul Walmsley , kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, Anup Patel , linux-mips@vger.kernel.org, Palmer Dabbelt , kvm-riscv@lists.infradead.org, Paolo Bonzini , Tianrui Zhao , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, May 21, 2024 at 06:40:08PM -0700, Sean Christopherson wrote: > Add a kvm_vcpu.scheduled_out flag to track if a vCPU is in the process of > being scheduled out (vCPU put path), or if the vCPU is being reloaded > after being scheduled out (vCPU load path). In the short term, this will > allow dropping kvm_arch_sched_in(), as arch code can query scheduled_out > during kvm_arch_vcpu_load(). > > Longer term, scheduled_out opens up other potential optimizations, without > creating subtle/brittle dependencies. E.g. it allows KVM to keep guest > state (that is managed via kvm_arch_vcpu_{load,put}()) loaded across > kvm_sched_{out,in}(), if KVM knows the state isn't accessed by the host > kernel. Forcing arch code to coordinate between kvm_arch_sched_{in,out}() > and kvm_arch_vcpu_{load,put}() is awkward, not reusable, and relies on the > exact ordering of calls into arch code. > > Adding scheduled_out also obviates the need for a kvm_arch_sched_out() > hook, e.g. if arch code needs to do something novel when putting vCPU > state. > > And even if KVM never uses scheduled_out for anything beyond dropping > kvm_arch_sched_in(), just being able to remove all of the arch stubs makes > it worth adding the flag. > > Link: https://lore.kernel.org/all/20240430224431.490139-1-seanjc@google.com > Cc: Oliver Upton > Signed-off-by: Sean Christopherson Reviewed-by: Oliver Upton -- Thanks, Oliver