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MFC: r269051

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Copying pages via temporary mappings in the !DMAP case of pmap_copy_pages()
involves updating the corresponding page tables followed by accesses to the
pages in question. This sequence is subject to the situation exactly described
in the "AMD64 Architecture Programmer's Manual Volume 2: System Programming"
rev. 3.23, "7.3.1 Special Coherency Considerations" [1, p. 171 f.]. Therefore,
issuing the INVLPG right after modifying the PTE bits is crucial (see also
r269050, MFCed to stable/10 in r269235).
For the amd64 PMAP code, the order of instructions was already correct. The
above fact still is worth documenting, though.

1: http://amd-dev.wpengine.netdna-cdn.com/wordpress/media/2012/10/24593_APM_v21.pdf

Reviewed by:	alc
Sponsored by:	Bally Wulff Games & Entertainment GmbH
This commit is contained in:
marius 2014-07-29 13:11:37 +00:00
parent 4f9788cb2b
commit 6b4298527d
1 changed files with 8 additions and 0 deletions
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8
sys/amd64/amd64/pmap.c
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@ -4984,6 +4984,14 @@ pmap_copy_pages(vm_page_t ma[], vm_offset_t a_offset, vm_page_t mb[],
int cnt;
boolean_t pinned;
/*
* NB: The sequence of updating a page table followed by accesses
* to the corresponding pages used in the !DMAP case is subject to
* the situation described in the "AMD64 Architecture Programmer's
* Manual Volume 2: System Programming" rev. 3.23, "7.3.1 Special
* Coherency Considerations". Therefore, issuing the INVLPG right
* after modifying the PTE bits is crucial.
*/
pinned = FALSE;
while (xfersize > 0) {
a_pg_offset = a_offset & PAGE_MASK;