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[PATCH] Argo: don't obtain excess page references
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 11 Oct 2022 11:28:06 +0200
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- Cc: Christopher Clark <christopher.w.clark@xxxxxxxxx>
- Delivery-date: Tue, 11 Oct 2022 09:28:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
find_ring_mfn() already holds a page reference when trying to obtain a
writable type reference. We shouldn't make assumptions on the general
reference count limit being effectively "infinity". Obtain merely a type
ref, re-using the general ref by only dropping the previously acquired
one in the case of an error.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I further question the log-dirty check there: The present P2M type of a
page doesn't really matter for writing to the page (plus it's stale by
the time it is looked at). Instead I think every write to such a page
needs to be accompanied by a call to paging_mark_dirty().
--- a/xen/common/argo.c
+++ b/xen/common/argo.c
@@ -1429,10 +1429,11 @@ find_ring_mfn(struct domain *d, gfn_t gf
ret = -EAGAIN;
#endif
else if ( (p2mt != p2m_ram_rw) ||
- !get_page_and_type(page, d, PGT_writable_page) )
+ !get_page_type(page, PGT_writable_page) )
ret = -EINVAL;
- put_page(page);
+ if ( unlikely(ret) )
+ put_page(page);
return ret;
}
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