vfio/type1: Improve memory pinning process for raw PFN mapping
When using vfio to pass through a PCIe device (e.g. a GPU card) that has a huge BAR (e.g. 16GB), a lot of cycles are wasted on memory pinning because PFNs of PCI BAR are not backed by struct page, and the corresponding VMA has flag VM_PFNMAP. With this change, when pinning a region which is a raw PFN mapping, it can skip unnecessary user memory pinning process, and thus, can significantly improve VM's boot up time when passing through devices via VFIO. In my test on a Xeon E5 2.6GHz, the time mapping a 16GB BAR was reduced from about 0.4s to 1.5us. Signed-off-by: Jason Cai (Xiang Feng) <jason.cai@linux.alibaba.com> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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@ -404,7 +404,6 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
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{
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unsigned long pfn = 0;
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long ret, pinned = 0, lock_acct = 0;
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bool rsvd;
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dma_addr_t iova = vaddr - dma->vaddr + dma->iova;
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/* This code path is only user initiated */
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@ -415,14 +414,23 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
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if (ret)
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return ret;
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if (is_invalid_reserved_pfn(*pfn_base)) {
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struct vm_area_struct *vma;
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down_read(¤t->mm->mmap_sem);
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vma = find_vma_intersection(current->mm, vaddr, vaddr + 1);
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pinned = min_t(long, npage, vma_pages(vma));
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up_read(¤t->mm->mmap_sem);
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return pinned;
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}
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pinned++;
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rsvd = is_invalid_reserved_pfn(*pfn_base);
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/*
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* Reserved pages aren't counted against the user, externally pinned
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* pages are already counted against the user.
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*/
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if (!rsvd && !vfio_find_vpfn(dma, iova)) {
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if (!vfio_find_vpfn(dma, iova)) {
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if (!lock_cap && current->mm->locked_vm + 1 > limit) {
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put_pfn(*pfn_base, dma->prot);
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pr_warn("%s: RLIMIT_MEMLOCK (%ld) exceeded\n", __func__,
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@ -442,13 +450,12 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
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if (ret)
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break;
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if (pfn != *pfn_base + pinned ||
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rsvd != is_invalid_reserved_pfn(pfn)) {
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if (pfn != *pfn_base + pinned) {
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put_pfn(pfn, dma->prot);
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break;
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}
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if (!rsvd && !vfio_find_vpfn(dma, iova)) {
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if (!vfio_find_vpfn(dma, iova)) {
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if (!lock_cap &&
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current->mm->locked_vm + lock_acct + 1 > limit) {
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put_pfn(pfn, dma->prot);
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@ -466,10 +473,8 @@ out:
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unpin_out:
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if (ret) {
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if (!rsvd) {
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for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
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put_pfn(pfn, dma->prot);
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}
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for (pfn = *pfn_base ; pinned ; pfn++, pinned--)
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put_pfn(pfn, dma->prot);
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return ret;
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}
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