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Fri, 29 May 2020 10:41:45 +0100 MIME-Version: 1.0 Date: Fri, 29 May 2020 10:41:44 +0100 From: Marc Zyngier To: Gavin Shan Subject: Re: [PATCH RFCv2 9/9] arm64: Support async page fault In-Reply-To: <6a4a82a4-af01-98c2-c854-9199f55f7bd3@redhat.com> References: <20200508032919.52147-1-gshan@redhat.com> <20200508032919.52147-10-gshan@redhat.com> <81adf013-3de7-23e6-7648-8aec821b033c@redhat.com> <8ab64c6a-582b-691d-79ab-21cdc0455cd3@redhat.com> <6a4a82a4-af01-98c2-c854-9199f55f7bd3@redhat.com> User-Agent: Roundcube Webmail/1.4.4 Message-ID: <6965aaf641a23fab64fbe2ceeb790272@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: gshan@redhat.com, pbonzini@redhat.com, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, shan.gavin@gmail.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: catalin.marinas@arm.com, linux-kernel@vger.kernel.org, shan.gavin@gmail.com, Paolo Bonzini , will@kernel.org, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: base64 Content-Type: text/plain; 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Fri, 29 May 2020 09:41:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590745306; bh=7656s4eYWhYzzAhobQ/p864RjB2diU/xpekCGE7YNZ0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=VQmr+kTgz6xT6jL5yWNdjI6CmqoEcxAQUP7Yjg5gfK3TvAVPbNdb45ezQRJ9TGm5G TYEBNnIFHaH7aClx19eT+daZr2aERlM073SlgHsQTree3AC6yibKxy1OhiiSgkbohN obMAXKU++5wiqUu1N0nZETdr3VtZjSVNHuHPj2mA= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jebWK-00GEXJ-Vz; Fri, 29 May 2020 10:41:45 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Fri, 29 May 2020 10:41:44 +0100 From: Marc Zyngier To: Gavin Shan Cc: Paolo Bonzini , kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, shan.gavin@gmail.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH RFCv2 9/9] arm64: Support async page fault In-Reply-To: <6a4a82a4-af01-98c2-c854-9199f55f7bd3@redhat.com> References: <20200508032919.52147-1-gshan@redhat.com> <20200508032919.52147-10-gshan@redhat.com> <81adf013-3de7-23e6-7648-8aec821b033c@redhat.com> <8ab64c6a-582b-691d-79ab-21cdc0455cd3@redhat.com> <6a4a82a4-af01-98c2-c854-9199f55f7bd3@redhat.com> User-Agent: Roundcube Webmail/1.4.4 Message-ID: <6965aaf641a23fab64fbe2ceeb790272@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: gshan@redhat.com, pbonzini@redhat.com, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, shan.gavin@gmail.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-05-29 00:02, Gavin Shan wrote: > Hi Paolo, > > On 5/28/20 8:48 PM, Paolo Bonzini wrote: >> On 28/05/20 08:14, Gavin Shan wrote: >>>> - for x86 we're also thinking of initiating the page fault from the >>>> exception handler, rather than doing so from the hypervisor before >>>> injecting the exception.  If ARM leads the way here, we would do our >>>> best to share code when x86 does the same. >>> >>> Sorry, Paolo, I don't follow your idea here. Could you please provide >>> more details? >> >> The idea is to inject stage2 page faults into the guest even before >> the >> host starts populates the page. The guest then invokes a hypercall, >> telling the host to populate the page table and inject the 'page >> ready' >> event (interrupt) when it's done. >> >> For x86 the advantage is that the processor can take care of raising >> the >> stage2 page fault in the guest, so it's faster. >> > I think there might be too much overhead if the page can be populated > quickly by host. For example, it's fast to populate the pages if swapin > isn't involved. > > If I'm correct enough, it seems arm64 doesn't have similar mechanism, > routing stage2 page fault to guest. Indeed, this isn't a thing on arm64. Exception caused by a S2 fault are always routed to EL2. M. -- Jazz is not dead. It just smells funny...