On Wed, Feb 14, 2018 at 2:13 PM, Tycho Andersen <tycho@xxxxxxxx> wrote: > On Wed, Feb 14, 2018 at 11:48:38AM -0800, Kees Cook wrote: >> On Wed, Feb 14, 2018 at 11:06 AM, Laura Abbott <labbott@xxxxxxxxxx> wrote: >> > fixed. Modules yes are not fully protected. The conclusion from past >> > experience has been that we cannot safely break down larger page sizes >> > at runtime like x86 does. We could theoretically >> > add support for fixing up the alias if PAGE_POISONING is enabled but >> > I don't know who would actually use that in production. Performance >> > is very poor at that point. >> >> XPFO forces 4K pages on the physmap[1] for similar reasons. I have no >> doubt about performance changes, but I'd be curious to see real >> numbers. Did anyone do benchmarks on just the huge/4K change? (Without >> also the XPFO overhead?) >> >> If this, XPFO, and PAGE_POISONING all need it, I think we have to >> start a closer investigation. :) > > I haven't but it shouldn't be too hard. What benchmarks are you > thinking? Unless I'm looking at some specific micro benchmark, I tend to default to looking at kernel build benchmarks but that gets pretty noisy. Laura regularly uses hackbench, IIRC. I'm not finding the pastebin I had for that, though. I wonder if we need a benchmark subdirectory in tools/testing/, so we could collect some of these common tools? All benchmarks are terrible, but at least we'd have the same terrible benchmarks. :) -Kees -- Kees Cook Pixel Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
