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bh=LkcPNNpMLX6kEqUed20/jhdzhJZXy+qPlqOir1Z4UWg=; b=oh6UumPZXvVAZaso7oC+mKwmmgkjeVHFpa4nQcJ1Rhwos8N77Zl7jnPJlsNH1BBcrj 5a20ooMYwFDAc0Yqyn63gJA5hYs7kdJO+jajzumIBN+h+9gO2y4LrrqH5mLuMzF74GT9 gnAVcoK5sR6kCXZn210jNq/RXq0tEJ2v55fkZbfktTTZ06uRXQJFq6B5rk9+VtgQbcF1 OtJ49i8spB14wm0fJ3lyOidlugFIsFTHeo4PGQ5X9Qh6TW4aXZhCHRSe7mm7VrsdKiGV zco5rPlSkBoEPmkDSpaeA6zB06qAFIDDzCrEB1PN16QoS4yoGvCD2SYLups6YouqTIew 38Dw== X-Gm-Message-State: AOAM531ysawkdZVQSA08XGZLVyQiF59vD2XX4JnxEiFGD5zcl4PxE0HJ 3mxoWbzZR+dNomS+126ELX3359ay3KsQegDVQ3mF+Q== X-Google-Smtp-Source: ABdhPJw6fgeaE8WrMv6/yjTLi0nLsEgIsTJGq7lnieyfjRKsxeZQjFjVvPlXPA1vJ6n1s7o3wIRvF8cXTGM5e/OE7rM= X-Received: by 2002:a05:6830:1647:: with SMTP id h7mr13325941otr.281.1604335352341; Mon, 02 Nov 2020 08:42:32 -0800 (PST) MIME-Version: 1.0 References: <20201030100815.2269-1-daniel.vetter@ffwll.ch> <20201030100815.2269-9-daniel.vetter@ffwll.ch> <20201102072931.GA16419@infradead.org> <20201102130115.GC36674@ziepe.ca> <20201102155256.GG36674@ziepe.ca> In-Reply-To: <20201102155256.GG36674@ziepe.ca> From: Daniel Vetter Date: Mon, 2 Nov 2020 17:42:20 +0100 Message-ID: Subject: Re: [PATCH v5 08/15] mm: Add unsafe_follow_pfn To: Jason Gunthorpe X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201102_114236_629240_429C61EC X-CRM114-Status: GOOD ( 26.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-samsung-soc , Jan Kara , Kees Cook , KVM list , John Hubbard , LKML , DRI Development , Christoph Hellwig , Linux MM , J??r??me Glisse , Daniel Vetter , Dan Williams , Andrew Morton , Linux ARM , "open list:DMA BUFFER SHARING FRAMEWORK" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Nov 2, 2020 at 4:52 PM Jason Gunthorpe wrote: > > On Mon, Nov 02, 2020 at 02:23:58PM +0100, Daniel Vetter wrote: > > On Mon, Nov 2, 2020 at 2:01 PM Jason Gunthorpe wrote: > > > > > > On Mon, Nov 02, 2020 at 01:56:10PM +0100, Daniel Vetter wrote: > > > > On Mon, Nov 2, 2020 at 8:29 AM Christoph Hellwig wrote: > > > > > > > > > > On Fri, Oct 30, 2020 at 11:08:08AM +0100, Daniel Vetter wrote: > > > > > > Also mark up follow_pfn as EXPORT_SYMBOL_GPL. The only safe way to use > > > > > > that by drivers/modules is together with an mmu_notifier, and that's > > > > > > all _GPL stuff. > > > > > > > > > > I also think it also needs to be renamed to explicitly break any existing > > > > > users out of tree or int the submission queue. > > > > > > > > Ok I looked at the mmu notifier locking again and noticed that > > > > mm->subscriptions has its own spinlock. Since there usually shouldn't > > > > be a huge pile of these I think it's feasible to check for the mmu > > > > notifier in follow_pfn. And that would stuff this gap for good. I'll > > > > throw that on top as a final patch and see what people think. > > > > > > Probably the simplest is to just check mm_has_notifiers() when in > > > lockdep or something very simple like that > > > > lockdep feels wrong, was locking more at CONFIG_DEBUG_VM. And since > > generally you only have 1 mmu notifier (especially for kvm) I think we > > can also pay the 2nd cacheline miss and actually check the right mmu > > notifier is registered. > > Need to hold the lock to check that and there are two ways to register > notifiers these days, so it feels to expensive to me. Uh I mixed stuff up all along, struct mmu_notifier *subcription that all the mmu notifier users use has the ->mm pointer we want right there. That's good enough I think. Now I'm kinda lost in kvm code trying to wire it through, but it's looking ok-ish thus far :-) -Daniel > CH's 'export symbol only for kvm' really does seem the most robust way > to handle this though. > > Jason -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel