lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Wed, 25 Jun 2008 20:11:05 -0700 From: Jeremy Fitzhardinge <jeremy@...p.org> To: Dave Airlie <airlied@...il.com> CC: Keith Packard <keithp@...thp.com>, Dave Airlie <airlied@...ux.ie>, linux-kernel <linux-kernel@...r.kernel.org>, Nick Piggin <nickpiggin@...oo.com.au> Subject: Re: kmap_atomic_pfn for PCI BAR access? Dave Airlie wrote: > On Thu, Jun 26, 2008 at 11:18 AM, Jeremy Fitzhardinge <jeremy@...p.org> wrote: > >> Keith Packard wrote: >> >>> The graphics memory BAR is generally fairly good sized; on Intel chips, >>> it's between 256M and 1G (and growing). I want to write data into this >>> region from kernel space, but it's really too big to map the whole thing >>> into kernel address space, especially on 32-bit systems. ioremap is not >>> a good option here -- it's way too slow. >>> >>> With CONFIG_HIGHMEM enabled, I can use kmap_atomic_pfn (well, actually >>> the kmap_atomic_proc_pfn included in the DRM tree) and things work quite >>> well -- performance is good, with barely any measurable time spent in >>> the PTE whacking (~1%). >>> >>> However, with CONFIG_HIGHMEM disabled, there aren't any PTEs reserved >>> for this kind of mapping fun. This makes me suspect that abusing >>> kmap_atomic for this operation would not be appreciated. >>> Should I use kmap_atomic_pfn to reach my PCI BAR like this? >>> >>> Would it be reasonable to supply a patch that made this work even >>> without CONFIG_HIGHMEM? >>> >>> >> Usually people use ioremap to map device memory. Wouldn't that work in this >> case? >> >> > > "but it's really too big to map the whole thing > into kernel address space, especially on 32-bit systems. ioremap is not > a good option here -- it's way too slow." > > From the original mail. > Uh, yep. > doing tlb flush for iounmap is slow as all hell if you do it a lot, > and we can't afford to mmap the whole aperture it can 1GB. > Maybe Nick's vmap reimplementation would help here. It effectively allows you to map stuff into the vmalloc space, and do lazy tlb flushes to mitigate the cost of map/unmap. He posted the patches week or so ago. J -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists