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Sun, 15 Nov 2020 18:36:55 +0000 (UTC) IronPort-SDR: KTQfuLMds5UE1kYfomDqiNCbkRdY7JYjKZaegcld7r7faPCJmH85UP3HO9nbWl8O5TmEQom47g ubBmQ+QsAiTQ== X-IronPort-AV: E=McAfee;i="6000,8403,9806"; a="232289908" X-IronPort-AV: E=Sophos;i="5.77,480,1596524400"; d="scan'208";a="232289908" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Nov 2020 10:36:53 -0800 IronPort-SDR: Se/PPj6k5pLuMb1SOKkJWlA61D8sB7Vu3NsHwZyyDQeeMjc7qm2bmP6cqQJk1sr6RmDNh3lDPO Cxn3v29AJBSA== X-IronPort-AV: E=Sophos;i="5.77,480,1596524400"; d="scan'208";a="533184727" Received: from jlongun-mobl3.amr.corp.intel.com (HELO [10.209.102.30]) ([10.209.102.30]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Nov 2020 10:36:51 -0800 Subject: Re: [PATCH v41 10/24] mm: Add 'mprotect' hook to struct vm_operations_struct To: Matthew Wilcox , Jarkko Sakkinen Cc: x86@kernel.org, linux-sgx@vger.kernel.org, linux-kernel@vger.kernel.org, Sean Christopherson , linux-mm@kvack.org, Andrew Morton , Mel Gorman , Jethro Beekman , andriy.shevchenko@linux.intel.com, asapek@google.com, bp@alien8.de, cedric.xing@intel.com, chenalexchen@google.com, conradparker@google.com, cyhanish@google.com, haitao.huang@intel.com, kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com, ludloff@google.com, luto@kernel.org, nhorman@redhat.com, npmccallum@redhat.com, puiterwijk@redhat.com, rientjes@google.com, tglx@linutronix.de, yaozhangx@google.com, mikko.ylinen@intel.com References: <20201112220135.165028-1-jarkko@kernel.org> <20201112220135.165028-11-jarkko@kernel.org> <20201115173208.GR17076@casper.infradead.org> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20201115173208.GR17076@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 11/15/20 9:32 AM, Matthew Wilcox wrote: > On Fri, Nov 13, 2020 at 12:01:21AM +0200, Jarkko Sakkinen wrote: >> +++ b/include/linux/mm.h >> @@ -559,6 +559,13 @@ struct vm_operations_struct { >> void (*close)(struct vm_area_struct * area); >> int (*split)(struct vm_area_struct * area, unsigned long addr); >> int (*mremap)(struct vm_area_struct * area); >> + /* >> + * Called by mprotect() to make driver-specific permission >> + * checks before mprotect() is finalised. The VMA must not >> + * be modified. Returns 0 if eprotect() can proceed. >> + */ >=20 > This is the wrong place for this documentation, and it's absurdly > specific to your implementation. It should be in > Documentation/filesystems/locking.rst. I'll let you and Mel duke that one out: > https://lore.kernel.org/linux-mm/20201106100409.GD3371@techsingularity.= net/ As for 'locking.rst', I didn't even know that was there. It's also a _bit_ silly that we would depend on folks finding that for code like SGX that has nothing to do with filesystems. If we expect folks to update that, we need a comment spelling that out in the struct. The comment also _looks_ reasonably generic to me. None of the parameters can be modified, so the impact on the core mm code must only be from the result of the return code, even if the handler does some other magic in addition to plain checks. For one thing, I guess we could take the literal mention of "driver" out. vm_operations are certainly supplied by code that isn't a "driver" per se. >> + int (*mprotect)(struct vm_area_struct *vma, unsigned long start, >> + unsigned long end, unsigned long newflags); >> + >> + if (vma->vm_ops && vma->vm_ops->mprotect) >> + error =3D vma->vm_ops->mprotect(vma, nstart, tmp, newflags); >> + if (error) >> + goto out; >> + >> error =3D mprotect_fixup(vma, &prev, nstart, tmp, newflags); >> if (error) >> goto out; >> + >> nstart =3D tmp; >=20 > Spurious newline added. I don't actually think this is spurious. It ends up grouping the code into the logical chunks with the ->mprotect() and goto in one chunk and mprotect_fixup() and its goto in another. Without this newline, the two logical parts don't look separate. It's kinda hard to see with just the diff context, though.