Re: [PATCH 3/6] KVM: MMU: introduce gfn_to_page_atomic() and gfn_to_pfn_atomic()

From: Avi Kivity
Date: Tue Jun 15 2010 - 07:22:24 EST

On 06/15/2010 05:46 AM, Xiao Guangrong wrote:
Introduce gfn_to_page_atomic() and gfn_to_pfn_atomic(), those
functions is fast path and can used in atomic context, the later
patch will use those

@@ -942,6 +942,41 @@ unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)

+static pfn_t hva_to_pfn_atomic(struct kvm *kvm, unsigned long addr)
+ struct page *page[1];
+ int npages;
+ pfn_t pfn;
+ npages = __get_user_pages_fast(addr, 1, 1, page);
+ if (unlikely(npages != 1)) {
+ if (is_hwpoison_address(addr)) {
+ get_page(hwpoison_page);
+ return page_to_pfn(hwpoison_page);
+ }
+ get_page(bad_page);
+ return page_to_pfn(bad_page);
+ } else
+ pfn = page_to_pfn(page[0]);
+ return pfn;

Too much duplication. How about putting the tail end of the function in a common helper (with an inatomic flag)?

btw, is_hwpoison_address() is racy. While it looks up the address, some other task can unmap the page tables under us.


One way of fixing it is get_user_pages_ptes_fast(), which also returns the pte, also atomically. I want it for other reasons as well (respond to a read fault by gupping the page for read, but allowing write access if the pte indicates it is writeable).

error compiling committee.c: too many arguments to function

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