From: David Laight <David.Laight@ACULAB.COM>
To: 'Jan Kara' <jack@suse.cz>, Dan Williams <dan.j.williams@intel.com>
Cc: Jeff Smits <jeff.smits@intel.com>,
Matthew Wilcox <willy@infradead.org>,
Kees Cook <keescook@chromium.org>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Christoph Hellwig <hch@lst.de>
Subject: RE: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead
Date: Fri, 17 May 2019 09:06:26 +0000 [thread overview]
Message-ID: <2d8b1ba7890940bf8a512d4eef0d99b3@AcuMS.aculab.com> (raw)
In-Reply-To: <20190517084739.GB20550@quack2.suse.cz>
From: Jan Kara
> Sent: 17 May 2019 09:48
...
> So this last paragraph is not obvious to me as check_copy_size() does a lot
> of various checks in CONFIG_HARDENED_USERCOPY case. I agree that some of
> those checks don't make sense for PMEM pages but I'd rather handle that by
> refining check_copy_size() and check_object_size() functions to detect and
> appropriately handle pmem pages rather that generally skip all the checks
> in pmem_copy_from/to_iter(). And yes, every check in such hot path is going
> to cost performance but that's what user asked for with
> CONFIG_HARDENED_USERCOPY... Kees?
Except that all the distros enable it by default.
So you get the performance cost whether you (as a user) want it or not.
I've changed some of our code to use __get_user() to avoid
these stupid overheads.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
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WARNING: multiple messages have this Message-ID (diff)
From: David Laight <David.Laight@ACULAB.COM>
To: 'Jan Kara' <jack@suse.cz>, Dan Williams <dan.j.williams@intel.com>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
Jeff Moyer <jmoyer@redhat.com>, Ingo Molnar <mingo@redhat.com>,
Christoph Hellwig <hch@lst.de>, Al Viro <viro@zeniv.linux.org.uk>,
Thomas Gleixner <tglx@linutronix.de>,
Matthew Wilcox <willy@infradead.org>,
Jeff Smits <jeff.smits@intel.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>
Subject: RE: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead
Date: Fri, 17 May 2019 09:06:26 +0000 [thread overview]
Message-ID: <2d8b1ba7890940bf8a512d4eef0d99b3@AcuMS.aculab.com> (raw)
In-Reply-To: <20190517084739.GB20550@quack2.suse.cz>
From: Jan Kara
> Sent: 17 May 2019 09:48
...
> So this last paragraph is not obvious to me as check_copy_size() does a lot
> of various checks in CONFIG_HARDENED_USERCOPY case. I agree that some of
> those checks don't make sense for PMEM pages but I'd rather handle that by
> refining check_copy_size() and check_object_size() functions to detect and
> appropriately handle pmem pages rather that generally skip all the checks
> in pmem_copy_from/to_iter(). And yes, every check in such hot path is going
> to cost performance but that's what user asked for with
> CONFIG_HARDENED_USERCOPY... Kees?
Except that all the distros enable it by default.
So you get the performance cost whether you (as a user) want it or not.
I've changed some of our code to use __get_user() to avoid
these stupid overheads.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2019-05-17 9:06 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-17 0:33 [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead Dan Williams
2019-05-17 0:33 ` Dan Williams
2019-05-17 8:47 ` Jan Kara
2019-05-17 8:47 ` Jan Kara
2019-05-17 9:06 ` David Laight [this message]
2019-05-17 9:06 ` David Laight
2019-05-17 15:53 ` Kees Cook
2019-05-17 15:53 ` Kees Cook
2019-05-17 16:14 ` David Laight
2019-05-17 16:14 ` David Laight
2019-05-17 16:40 ` Kees Cook
2019-05-17 15:08 ` Dan Williams
2019-05-17 15:08 ` Dan Williams
2019-05-17 15:56 ` Kees Cook
2019-05-17 15:56 ` Kees Cook
2019-05-17 17:28 ` Dan Williams
2019-05-17 17:28 ` Dan Williams
2019-05-17 19:25 ` Kees Cook
2019-05-17 19:25 ` Kees Cook
2019-05-19 4:46 ` Dan Williams
2019-05-19 4:46 ` Dan Williams
2019-05-20 7:52 ` Jan Kara
2019-05-20 7:52 ` Jan Kara
2019-05-20 15:40 ` Dan Williams
2019-05-20 15:40 ` Dan Williams
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