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([2001:b07:6468:f312:3c1c:ffba:c624:29b8]) by smtp.gmail.com with ESMTPSA id b8sm14890619wrs.36.2020.05.30.09.20.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 30 May 2020 09:20:06 -0700 (PDT) Subject: Re: [PATCH 8/9] x86: kvm_hv_set_msr(): use __put_user() instead of 32bit __clear_user() To: Al Viro , Linus Torvalds Cc: Linux Kernel Mailing List , linux-fsdevel , KVM list References: <20200528234025.GT23230@ZenIV.linux.org.uk> <20200529232723.44942-1-viro@ZenIV.linux.org.uk> <20200529232723.44942-8-viro@ZenIV.linux.org.uk> <20200530143147.GN23230@ZenIV.linux.org.uk> From: Paolo Bonzini Message-ID: <81563af6-6ea2-3e21-fe53-9955910e303a@redhat.com> Date: Sat, 30 May 2020 18:20:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200530143147.GN23230@ZenIV.linux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Fri, May 29, 2020 at 04:52:59PM -0700, Linus Torvalds wrote: >> It looks like the argument for the address being validated is that it >> comes from "gfn_to_hva()", which should only return >> host-virtual-addresses. That may be true. Yes, the access_ok is done in __kvm_set_memory_region and gfn_to_hva() returns a page-aligned address so it's obviously ok for a u32. But I have no objections to removing the __ because if a read or write is in the hot path it will use kvm_write_guest_cached and similar. Paolo >> But "should" is not "does", and honestly, the cost of gfn_to_hva() is >> high enough that then using that as an argument for removing >> "access_ok()" smells.