Date: Thu, 3 Oct 2013 21:46:44 +0000 (UTC) From: Neel Natu <neel@FreeBSD.org> To: src-committers@freebsd.org, svn-src-projects@freebsd.org Subject: svn commit: r256031 - projects/bhyve_npt_pmap/sys/amd64/amd64 Message-ID: <201310032146.r93LkiBN047424@svn.freebsd.org>
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Author: neel Date: Thu Oct 3 21:46:43 2013 New Revision: 256031 URL: http://svnweb.freebsd.org/changeset/base/256031 Log: Add a comment in pmap_copy() explaining why we skip the function entirely for emulated pmaps. Requested by: alc@ Modified: projects/bhyve_npt_pmap/sys/amd64/amd64/pmap.c Modified: projects/bhyve_npt_pmap/sys/amd64/amd64/pmap.c ============================================================================== --- projects/bhyve_npt_pmap/sys/amd64/amd64/pmap.c Thu Oct 3 20:38:57 2013 (r256030) +++ projects/bhyve_npt_pmap/sys/amd64/amd64/pmap.c Thu Oct 3 21:46:43 2013 (r256031) @@ -4762,6 +4762,14 @@ pmap_copy(pmap_t dst_pmap, pmap_t src_pm if (dst_pmap->pm_type != src_pmap->pm_type) return; + /* + * EPT page table entries that require emulation of A/D bits are + * sensitive to clearing the PG_A bit (aka EPT_PG_READ). Although + * we clear PG_M (aka EPT_PG_WRITE) concomitantly, the PG_U bit + * (aka EPT_PG_EXECUTE) could still be set. Since some EPT + * implementations flag an EPT misconfiguration for exec-only + * mappings we skip this function entirely for emulated pmaps. + */ if (pmap_emulate_ad_bits(dst_pmap)) return;
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