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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 70913C433EF for ; Fri, 25 Feb 2022 17:00:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243431AbiBYRAm (ORCPT ); Fri, 25 Feb 2022 12:00:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243225AbiBYRAi (ORCPT ); Fri, 25 Feb 2022 12:00:38 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B81591D529C; Fri, 25 Feb 2022 09:00:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=GShWhJaDIDVMvbVdUPdxNafriM5wV3Zj7hmmN6XO+3Y=; b=UO0lWylllnOnJjQMlCj/cyNww3 jO+9WZsHmUEx74Z7f7tj/fMmCPgA+wmT8shE9QZEaGrRbntRlVbN60eO7Tr6y66aPE06jPgoLKPwZ kufOusN8EyzmzYenIHmZ/7kOLycBszfVCpEqeOAZqyivpDAYQ1jIHEA1OE/mmWo5ur+lqhe4dc1D2 QQBu4DKHyTFjFb+YAXIovynrK/d1+e8VN6hhWcf8dj4tlrCbf6VvHS++EUEfDfJD8G9BnyfR2CtpD +dZrGBLmRy5DzfR7ZtBcfz7XM1rcJA48a0AYYQDfP9QPNW620qe0X7tFUKTx4aNa1hOo9QqtI6lDY r7dwAjtg==; Received: from [2001:8b0:10b:1::3ae] (helo=u3832b3a9db3152.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nNdwm-005xah-7s; Fri, 25 Feb 2022 17:00:00 +0000 Message-ID: <915ddc7327585bbe8587b91b8cd208520d684db1.camel@infradead.org> Subject: Re: [EXTERNAL] [PATCH v2] KVM: Don't actually set a request when evicting vCPUs for GFN cache invd From: David Woodhouse To: Sean Christopherson Cc: "borntraeger@linux.ibm.com" , "pbonzini@redhat.com" , "frankja@linux.ibm.com" , "kvm@vger.kernel.org" , "imbrenda@linux.ibm.com" , "david@redhat.com" , "linux-kernel@vger.kernel.org" Date: Fri, 25 Feb 2022 16:59:59 +0000 In-Reply-To: References: <20220223165302.3205276-1-seanjc@google.com> <2547e9675d855449bc5cc7efb97251d6286a377c.camel@amazon.co.uk> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-dD9wpp1DUw6iChWn27LV" User-Agent: Evolution 3.36.5-0ubuntu1 MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-dD9wpp1DUw6iChWn27LV Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2022-02-25 at 16:13 +0000, Sean Christopherson wrote: > On Fri, Feb 25, 2022, Woodhouse, David wrote: > > Since we need an active vCPU context to do dirty logging (thanks, dirty > > ring)... and since any time vcpu_run exits to userspace for any reason > > might be the last time we ever get an active vCPU context... I think > > that kind of fundamentally means that we must flush dirty state to the > > log on *every* return to userspace, doesn't it? >=20 > I would rather add a variant of mark_page_dirty_in_slot() that takes a vC= PU, which > we whould have in all cases. I see no reason to require use of kvm_get_r= unning_vcpu(). We already have kvm_vcpu_mark_page_dirty(), but it can't use just 'some vcpu' because the dirty ring is lockless. So if you're ever going to use anything other than kvm_get_running_vcpu() we need to add locks. And while we *could* do that, I don't think it would negate the fundamental observation that *any* time we return from vcpu_run to userspace, that could be the last time. Userspace might read the dirty log for the *last* time, and any internally-cached "oh, at some point we need to mark page dirty" is lost because by the time the vCPU is finally destroyed, it's too late. I think I'm going to rip out the 'dirty' flag from the gfn_to_pfn_cache completely and add a function (to be called with an active vCPU context) which marks the page dirty *now*. KVM_GUEST_USES_PFN users like nested VMX will be expected to do this before returning from vcpu_run anytime it's in L2 guest mode.=20 --=-dD9wpp1DUw6iChWn27LV Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCEkQw ggYQMIID+KADAgECAhBNlCwQ1DvglAnFgS06KwZPMA0GCSqGSIb3DQEBDAUAMIGIMQswCQYDVQQG EwJVUzETMBEGA1UECBMKTmV3IEplcnNleTEUMBIGA1UEBxMLSmVyc2V5IENpdHkxHjAcBgNVBAoT FVRoZSBVU0VSVFJVU1QgTmV0d29yazEuMCwGA1UEAxMlVVNFUlRydXN0IFJTQSBDZXJ0aWZpY2F0 aW9uIEF1dGhvcml0eTAeFw0xODExMDIwMDAwMDBaFw0zMDEyMzEyMzU5NTlaMIGWMQswCQYDVQQG EwJHQjEbMBkGA1UECBMSR3JlYXRlciBNYW5jaGVzdGVyMRAwDgYDVQQHEwdTYWxmb3JkMRgwFgYD VQQKEw9TZWN0aWdvIExpbWl0ZWQxPjA8BgNVBAMTNVNlY3RpZ28gUlNBIENsaWVudCBBdXRoZW50 aWNhdGlvbiBhbmQgU2VjdXJlIEVtYWlsIENBMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKC AQEAyjztlApB/975Rrno1jvm2pK/KxBOqhq8gr2+JhwpKirSzZxQgT9tlC7zl6hn1fXjSo5MqXUf 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