[Xen-devel] [PATCH][Xen 4.0-testing.hg] fix small bugs of memory sharing

[Jui-Hao Chiang <juihaochiang@xxxxxxxxx>]

Hi, all:

xen/arch/x86/hvm/hvm.c        |   2 ++
xen/arch/x86/mm.c             |  20 ++++++++++----------
xen/arch/x86/mm/mem_sharing.c |   4 ++--
3 files changed, 14 insertions(+), 12 deletions(-)

This small patch fixes 2 problems of memory sharing for xen-4.0-testing.hg
(I haven't submitted patch here, if it violates any conventional rules, I'm glad to have advices)
(1)  When nominating a shared page, the page_make_sharable() does not recover the type_info count if it fails to nominate the page.

(2) When building xen with debug=n, the code in ASSERT() won't get executed. Change to BUG_ON.

Besides, I don't understand why the page_make_sharable() force checking the count_info with the following way?
/* Check if the ref count is 2. The first from PGT_allocated, and the second
     * from get_page at the top of this function */
    if(page->count_info != (PGC_allocated | (2 + expected_refcnt)))

This seems to imply that the following kind of page can never be nominated for shared pages because ci (count_info) is greater than 2 after get_page. Here, domain 3 is a 64-bit HVM with hap=1, pae=1 on 64bit Xen.
(XEN) Debug for domain=3, gfn=10, Debug page: MFN=c210ad is ci=8000000000000002, ti=0, owner_id=3

Can someone gives a hint that
(1) in what kind of scenario that ci = 2 and ti=0?
(2) or why not allow ci >=2 to be nominated?

Bests,
Jui-Hao Chiang at CCMA, ITRI, R.O.C

Attachment: xen-4.0-testing.hg.mem_sharing.patch
Description: Text Data

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