Date: Tue, 6 Jun 2017 18:07:10 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Hans Petter Selasky <hps@selasky.org> Cc: Allan Jude <allanjude@FreeBSD.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r316311 - in head: lib/libstand sys/boot/geli sys/boot/i386/gptboot sys/boot/i386/loader sys/boot/i386/zfsboot Message-ID: <20170606150710.GF2088@kib.kiev.ua> In-Reply-To: <85ee6ae1-f934-caf6-a219-3d9901f3d277@selasky.org> References: <201703310004.v2V04W3A043449@repo.freebsd.org> <85ee6ae1-f934-caf6-a219-3d9901f3d277@selasky.org>
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On Tue, Jun 06, 2017 at 03:51:26PM +0200, Hans Petter Selasky wrote: > On 03/31/17 02:04, Allan Jude wrote: > > Author: allanjude > > Date: Fri Mar 31 00:04:32 2017 > > New Revision: 316311 > > URL: https://svnweb.freebsd.org/changeset/base/316311 > > > > > > > > Modified: head/sys/boot/i386/zfsboot/zfsboot.c > > ============================================================================== > > --- head/sys/boot/i386/zfsboot/zfsboot.c Thu Mar 30 23:49:57 2017 (r316310) > > +++ head/sys/boot/i386/zfsboot/zfsboot.c Fri Mar 31 00:04:32 2017 (r316311) > > @@ -926,7 +926,7 @@ load(void) > > zfsargs.primary_pool = primary_spa->spa_guid; > > #ifdef LOADER_GELI_SUPPORT > > bcopy(gelipw, zfsargs.gelipw, sizeof(zfsargs.gelipw)); > > - bzero(gelipw, sizeof(gelipw)); > > + explicit_bzero(gelipw, sizeof(gelipw)); > > #else > > zfsargs.gelipw[0] = '\0'; > > #endif > > > > Hi Allan, > > For ARM platforms you'll need to do a write memory barrier before the > explicit_bzero() returns, else the memory can be recovered by > invalidating the memory area by the next thread which is allocating this > memory ??? Note that loader execution is single threaded / single core. As is, it is not possible for the cache invalidation targeting the generic memory in loader to occur. That said, if we consider usage of the explicit_bzero() in more complete environment, then a memory barrier is definitely useless for the stated purpose. After the writing thread issued a barrier, cache is not flushed to RAM. In other words, cache flush is probably worth doing there, as you noted. But this raises a question, shouldn't the explicit_bzero() implementation handle the cache flush ?
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