Date: Tue, 1 Oct 2019 15:33:47 +0000 (UTC) From: Alan Cox <alc@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r352930 - head/sys/arm64/arm64 Message-ID: <201910011533.x91FXluG064105@repo.freebsd.org>
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Author: alc Date: Tue Oct 1 15:33:47 2019 New Revision: 352930 URL: https://svnweb.freebsd.org/changeset/base/352930 Log: In short, pmap_enter_quick_locked("user space", ..., VM_PROT_READ) doesn't work. More precisely, it doesn't set ATTR_AP(ATTR_AP_USER) in the page table entry, so any attempt to read from the mapped page by user space generates a page fault. This problem has gone unnoticed because the page fault handler, vm_fault(), will ultimately call pmap_enter(), which replaces the non-working page table entry with one that has ATTR_AP(ATTR_AP_USER) set. This change reduces the number of page faults during a "buildworld" by about 19.4%. Reviewed by: andrew, markj MFC after: 1 week Differential Revision: https://reviews.freebsd.org/D21841 Modified: head/sys/arm64/arm64/pmap.c Modified: head/sys/arm64/arm64/pmap.c ============================================================================== --- head/sys/arm64/arm64/pmap.c Tue Oct 1 15:10:35 2019 (r352929) +++ head/sys/arm64/arm64/pmap.c Tue Oct 1 15:33:47 2019 (r352930) @@ -3752,8 +3752,8 @@ pmap_enter_quick_locked(pmap_t pmap, vm_offset_t va, v ATTR_AP(ATTR_AP_RO) | L3_PAGE; if ((prot & VM_PROT_EXECUTE) == 0 || m->md.pv_memattr == DEVICE_MEMORY) l3_val |= ATTR_XN; - else if (va < VM_MAXUSER_ADDRESS) - l3_val |= ATTR_PXN; + if (va < VM_MAXUSER_ADDRESS) + l3_val |= ATTR_AP(ATTR_AP_USER) | ATTR_PXN; /* * Now validate mapping with RO protection
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