Date: Fri, 31 Jan 2020 01:37:34 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: "freebsd-current@FreeBSD.org" <freebsd-current@freebsd.org> Subject: Re: easy way to work around a lack of a direct map on i386 Message-ID: <20200130233734.GV4808@kib.kiev.ua> In-Reply-To: <YTBPR01MB3374AA25792499A796DB7CAADD040@YTBPR01MB3374.CANPRD01.PROD.OUTLOOK.COM>
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On Thu, Jan 30, 2020 at 11:23:02PM +0000, Rick Macklem wrote: > Hi, > > The current code for KERN_TLS uses PHYS_TO_DMAP() > to access unmapped external pages on m_ext.ext_pgs > mbufs. > I also need to do this to implement RPC-over-TLS. > > The problem is that some arches, like i386, don't > support PHYS_TO_DMAP(). > > Since it appears that there will be at most 4 pages on > one of these mbufs, my thinking was... > - Acquire four pages of kva from the kernel_map during > booting. > - Then just use pmap_qenter() to fill in the physical page > mappings for long enough to copy the data. > > Does this sound reasonable? > Is there a better way? Use sfbufs, they should work on all arches. In essence, they provide MI interface to DMAP where possible. I do not remember did I bumped the limit for i386 after 4/4 went in. There is currently no limits for sfbufs use per subsystem, but I think it is not very likely to cause too much troubles. Main rule is to not sleep waiting for more sfbufs if you already own one..home | help
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