KVM: try __get_user_pages_fast even if not in atomic context
We are currently cutting hva_to_pfn_fast short if we do not want an immediate exit, which is represented by !async && !atomic. However, this is unnecessary, and __get_user_pages_fast is *much* faster because the regular get_user_pages takes pmd_lock/pte_lock. In fact, when many CPUs take a nested vmexit at the same time the contention on those locks is visible, and this patch removes about 25% (compared to 4.18) from vmexit.flat on a 16 vCPU nested guest. Suggested-by: Andrea Arcangeli <aarcange@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>hifive-unleashed-5.1
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@ -1343,18 +1343,16 @@ static inline int check_user_page_hwpoison(unsigned long addr)
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}
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}
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/*
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/*
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* The atomic path to get the writable pfn which will be stored in @pfn,
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* The fast path to get the writable pfn which will be stored in @pfn,
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* true indicates success, otherwise false is returned.
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* true indicates success, otherwise false is returned. It's also the
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* only part that runs if we can are in atomic context.
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*/
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*/
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static bool hva_to_pfn_fast(unsigned long addr, bool atomic, bool *async,
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static bool hva_to_pfn_fast(unsigned long addr, bool write_fault,
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bool write_fault, bool *writable, kvm_pfn_t *pfn)
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bool *writable, kvm_pfn_t *pfn)
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{
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{
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struct page *page[1];
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struct page *page[1];
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int npages;
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int npages;
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if (!(async || atomic))
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return false;
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/*
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/*
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* Fast pin a writable pfn only if it is a write fault request
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* Fast pin a writable pfn only if it is a write fault request
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* or the caller allows to map a writable pfn for a read fault
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* or the caller allows to map a writable pfn for a read fault
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@ -1498,7 +1496,7 @@ static kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
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/* we can do it either atomically or asynchronously, not both */
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/* we can do it either atomically or asynchronously, not both */
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BUG_ON(atomic && async);
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BUG_ON(atomic && async);
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if (hva_to_pfn_fast(addr, atomic, async, write_fault, writable, &pfn))
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if (hva_to_pfn_fast(addr, write_fault, writable, &pfn))
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return pfn;
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return pfn;
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if (atomic)
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if (atomic)
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