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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id x24sm12795492qkx.23.2020.11.24.07.55.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Nov 2020 07:55:27 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1khaf8-000pJU-UM; Tue, 24 Nov 2020 11:55:26 -0400 Date: Tue, 24 Nov 2020 11:55:26 -0400 From: Jason Gunthorpe To: DRI Development , LKML , kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, Daniel Vetter , Christoph Hellwig , Kees Cook , Dan Williams , Andrew Morton , John Hubbard , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara Subject: Re: [PATCH v6 17/17] RFC: mm: add mmu_notifier argument to follow_pfn Message-ID: <20201124155526.GH5487@ziepe.ca> References: <20201119144146.1045202-1-daniel.vetter@ffwll.ch> <20201119144146.1045202-18-daniel.vetter@ffwll.ch> <20201120183029.GQ244516@ziepe.ca> <20201124142814.GM401619@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201124142814.GM401619@phenom.ffwll.local> Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Tue, Nov 24, 2020 at 03:28:14PM +0100, Daniel Vetter wrote: > On Fri, Nov 20, 2020 at 02:30:29PM -0400, Jason Gunthorpe wrote: > > On Thu, Nov 19, 2020 at 03:41:46PM +0100, Daniel Vetter wrote: > > > @@ -4805,21 +4824,15 @@ EXPORT_SYMBOL(follow_pte_pmd); > > > * Return: zero and the pfn at @pfn on success, -ve otherwise. > > > */ > > > int follow_pfn(struct vm_area_struct *vma, unsigned long address, > > > - unsigned long *pfn) > > > + unsigned long *pfn, struct mmu_notifier *subscription) > > > { > > > - int ret = -EINVAL; > > > - spinlock_t *ptl; > > > - pte_t *ptep; > > > + if (WARN_ON(!subscription->mm)) > > > + return -EINVAL; > > > > > > + if (WARN_ON(subscription->mm != vma->vm_mm)) > > > + return -EINVAL; > > > > These two things are redundant right? vma->vm_mm != NULL? > > Yup, will remove. > > > BTW, why do we even have this for nommu? If the only caller is kvm, > > can you even compile kvm on nommu?? > > Kinda makes sense, but I have no idea how to make sure with compile > testing this is really the case. And I didn't see any hard evidence in > Kconfig or Makefile that mmu notifiers requires CONFIG_MMU. So not sure > what to do here. It looks like only some arches have selectable CONFIG_MMU: arm, m68k, microblaze, riscv, sh If we look at arches that work with HAVE_KVM, I only see: arm64, mips, powerpc, s390, x86 So my conclusion is there is no intersection between !MMU and HAVE_KVM? > Should I just remove the nommu version of follow_pfn and see what happens? > We can't remove it earlier since it's still used by other > subsystems. This is what I was thinking might work Jason