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Date: Sat, 13 Feb 2010 21:12:08 -0800 From: "H. Peter Anvin" <hpa@...or.com> To: Suresh Siddha <suresh.b.siddha@...el.com> CC: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "rostedt@...dmis.org" <rostedt@...dmis.org>, "jeremy@...p.org" <jeremy@...p.org> Subject: Re: [PATCH] x86_64: allow sections that are recycled to set _PAGE_RW On 02/13/2010 12:08 PM, Suresh Siddha wrote: > > Checks in static_protections() ensure that we map the text mapping as > read-only (and don't bother about what permissions it uses for > underlying free pages that get freed in free_init_pages()). But the > kernel direct mappings for free pages will be RW and ensure that the > free pages can be read/written using the direct mapping. > > The checks in static_protections() for kernel text mapping ensure that > we don't break the 2MB kernel text pages unnecessarily on 64bit kernels > (as it has performance implications). We should be fine as long as the > kernel identity mappings reflect the correct RW permissions. > > But somehow this is working fine on native kernels but not on Xen pv > guest. Your patch will cause the performance issues that we are > addressing using the static protections checks. I will look at this more > detailed on tuesday. > Xen doesn't support PSE, so it has the (otherwise impossible) combination of PAE and !PSE ... i.e. it only uses 4K pages. -hpa -- 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/
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