From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752001AbbDHKnV (ORCPT ); Wed, 8 Apr 2015 06:43:21 -0400 Received: from mx1.redhat.com ([209.132.183.28]:32830 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751132AbbDHKnT (ORCPT ); Wed, 8 Apr 2015 06:43:19 -0400 Message-ID: <55250643.3090402@redhat.com> Date: Wed, 08 Apr 2015 12:43:15 +0200 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0 MIME-Version: 1.0 To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= CC: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [PATCH] KVM: dirty all pages in kvm_write_guest_cached() References: <1428438897-22206-1-git-send-email-rkrcmar@redhat.com> <5524EBB7.3080906@redhat.com> <20150408092611.GA2164@potion.brq.redhat.com> In-Reply-To: <20150408092611.GA2164@potion.brq.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/04/2015 11:26, Radim Krčmář wrote: > 2015-04-08 10:49+0200, Paolo Bonzini: >> On 07/04/2015 22:34, Radim Krčmář wrote: >>> We dirtied only one page because writes originally couldn't span more. >>> Use improved syntax for '>> PAGE_SHIFT' while at it. >>> >>> Fixes: 8f964525a121 ("KVM: Allow cross page reads and writes from cached translations.") >>> Signed-off-by: Radim Krčmář >> >> Cross-page reads and writes should never get here; they have >> ghc->memslot set to NULL and go through the slow path in kvm_write_guest. > > Only cross-memslot writes have NULL memslot. The power of wrong comments... Considering how kvm_gfn_to_hva_cache_init is used (one 1-byte field, two 4-byte fields, one 28-bytes struct that is 32-bytes aligned, one 32-bytes field that is in practice cacheline-aligned), I wonder if we should just use ghc->memslot = NULL for cross page writes. This would bypass the bug you are fixing here, and avoid worries about partial writes. Paolo