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From: Avi Kivity on 15 Jun 2010 07:30
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)
> }
> EXPORT_SYMBOL_GPL(gfn_to_hva);
>
> +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.

Andi/Huang?

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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From: Xiao Guangrong on 17 Jun 2010 02:50


Avi Kivity wrote:
> 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)
>> }
>> EXPORT_SYMBOL_GPL(gfn_to_hva);
>>
>> +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)?
>

OK, will cleanup it in the next version.
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