"Aneesh Kumar K.V" <aneesh.ku...@linux.ibm.com> writes:
> The current code doesn't do page migration if the page allocated is a
> compound page.
> With HugeTLB migration support, we can end up allocating hugetlb pages from
> CMA region. Also, THP pages can be allocated from CMA region. This patch
> updates
> the code to handle compound pages correctly. The patch also switches to a
> single
> get_user_pages with the right count, instead of doing one get_user_pages per
> page.
> That avoids reading page table multiple times.
It's not very obvious from the above description that the migration
logic is now being done by get_user_pages_longterm(), it just looks like
it's all being deleted in this patch. Would be good to mention that.
> Since these page reference updates are long term pin, switch to
> get_user_pages_longterm. That makes sure we fail correctly if the guest RAM
> is backed by DAX pages.
Can you explain that in more detail?
> The patch also converts the hpas member of mm_iommu_table_group_mem_t to a
> union.
> We use the same storage location to store pointers to struct page. We cannot
> update all the code path use struct page *, because we access hpas in real
> mode
> and we can't do that struct page * to pfn conversion in real mode.
That's a pain, it's asking for bugs mixing two different values in the
same array. But I guess it's the least worst option.
It sounds like that's a separate change you could do in a separate
patch. But it's not, because it's tied to the fact that we're doing a
single GUP call.
> diff --git a/arch/powerpc/mm/mmu_context_iommu.c
> b/arch/powerpc/mm/mmu_context_iommu.c
> index a712a650a8b6..f11a2f15071f 100644
> --- a/arch/powerpc/mm/mmu_context_iommu.c
> +++ b/arch/powerpc/mm/mmu_context_iommu.c
> @@ -21,6 +21,7 @@
> #include <linux/sizes.h>
> #include <asm/mmu_context.h>
> #include <asm/pte-walk.h>
> +#include <linux/mm_inline.h>
>
> static DEFINE_MUTEX(mem_list_mutex);
>
> @@ -34,8 +35,18 @@ struct mm_iommu_table_group_mem_t {
> atomic64_t mapped;
> unsigned int pageshift;
> u64 ua; /* userspace address */
> - u64 entries; /* number of entries in hpas[] */
> - u64 *hpas; /* vmalloc'ed */
> + u64 entries; /* number of entries in hpas/hpages[] */
> + /*
> + * in mm_iommu_get we temporarily use this to store
> + * struct page address.
> + *
> + * We need to convert ua to hpa in real mode. Make it
> + * simpler by storing physical address.
> + */
> + union {
> + struct page **hpages; /* vmalloc'ed */
> + phys_addr_t *hpas;
> + };
> #define MM_IOMMU_TABLE_INVALID_HPA ((uint64_t)-1)
> u64 dev_hpa; /* Device memory base address */
> };
> @@ -80,64 +91,15 @@ bool mm_iommu_preregistered(struct mm_struct *mm)
> }
> EXPORT_SYMBOL_GPL(mm_iommu_preregistered);
>
> -/*
> - * Taken from alloc_migrate_target with changes to remove CMA allocations
> - */
> -struct page *new_iommu_non_cma_page(struct page *page, unsigned long private)
> -{
> - gfp_t gfp_mask = GFP_USER;
> - struct page *new_page;
> -
> - if (PageCompound(page))
> - return NULL;
> -
> - if (PageHighMem(page))
> - gfp_mask |= __GFP_HIGHMEM;
> -
> - /*
> - * We don't want the allocation to force an OOM if possibe
> - */
> - new_page = alloc_page(gfp_mask | __GFP_NORETRY | __GFP_NOWARN);
> - return new_page;
> -}
> -
> -static int mm_iommu_move_page_from_cma(struct page *page)
> -{
> - int ret = 0;
> - LIST_HEAD(cma_migrate_pages);
> -
> - /* Ignore huge pages for now */
> - if (PageCompound(page))
> - return -EBUSY;
> -
> - lru_add_drain();
> - ret = isolate_lru_page(page);
> - if (ret)
> - return ret;
> -
> - list_add(&page->lru, &cma_migrate_pages);
> - put_page(page); /* Drop the gup reference */
> -
> - ret = migrate_pages(&cma_migrate_pages, new_iommu_non_cma_page,
> - NULL, 0, MIGRATE_SYNC, MR_CONTIG_RANGE);
> - if (ret) {
> - if (!list_empty(&cma_migrate_pages))
> - putback_movable_pages(&cma_migrate_pages);
> - }
> -
> - return 0;
> -}
> -
> static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
> - unsigned long entries, unsigned long dev_hpa,
> - struct mm_iommu_table_group_mem_t **pmem)
> + unsigned long entries, unsigned long dev_hpa,
> + struct mm_iommu_table_group_mem_t **pmem)
> {
> struct mm_iommu_table_group_mem_t *mem;
> - long i, j, ret = 0, locked_entries = 0;
> + long i, ret = 0, locked_entries = 0;
I'd prefer we didn't initialise ret here.
> unsigned int pageshift;
> unsigned long flags;
> unsigned long cur_ua;
> - struct page *page = NULL;
>
> mutex_lock(&mem_list_mutex);
>
> @@ -187,41 +149,27 @@ static long mm_iommu_do_alloc(struct mm_struct *mm,
> unsigned long ua,
> goto unlock_exit;
> }
>
> + down_read(&mm->mmap_sem);
> + ret = get_user_pages_longterm(ua, entries, FOLL_WRITE, mem->hpages,
> NULL);
> + up_read(&mm->mmap_sem);
> + if (ret != entries) {
> + /* free the reference taken */
> + for (i = 0; i < ret; i++)
> + put_page(mem->hpages[i]);
> +
> + vfree(mem->hpas);
> + kfree(mem);
> + ret = -EFAULT;
> + goto unlock_exit;
> + } else {
> + ret = 0;
Or here.
Instead it should be set to 0 at good_exit.
> + }
> +
> + pageshift = PAGE_SHIFT;
> for (i = 0; i < entries; ++i) {
> + struct page *page = mem->hpages[i];
> +
> cur_ua = ua + (i << PAGE_SHIFT);
> - if (1 != get_user_pages_fast(cur_ua,
> - 1/* pages */, 1/* iswrite */, &page)) {
> - ret = -EFAULT;
> - for (j = 0; j < i; ++j)
> - put_page(pfn_to_page(mem->hpas[j] >>
> - PAGE_SHIFT));
> - vfree(mem->hpas);
> - kfree(mem);
> - goto unlock_exit;
> - }
> - /*
> - * If we get a page from the CMA zone, since we are going to
> - * be pinning these entries, we might as well move them out
> - * of the CMA zone if possible. NOTE: faulting in + migration
> - * can be expensive. Batching can be considered later
> - */
> - if (is_migrate_cma_page(page)) {
> - if (mm_iommu_move_page_from_cma(page))
> - goto populate;
> - if (1 != get_user_pages_fast(cur_ua,
> - 1/* pages */, 1/* iswrite */,
> - &page)) {
> - ret = -EFAULT;
> - for (j = 0; j < i; ++j)
> - put_page(pfn_to_page(mem->hpas[j] >>
> - PAGE_SHIFT));
> - vfree(mem->hpas);
> - kfree(mem);
> - goto unlock_exit;
> - }
> - }
> -populate:
> - pageshift = PAGE_SHIFT;
> if (mem->pageshift > PAGE_SHIFT && PageCompound(page)) {
> pte_t *pte;
> struct page *head = compound_head(page);
> @@ -239,6 +187,10 @@ static long mm_iommu_do_alloc(struct mm_struct *mm,
> unsigned long ua,
> local_irq_restore(flags);
> }
> mem->pageshift = min(mem->pageshift, pageshift);
> + /*
> + * We don't need struct page reference any more, switch
> + * to physical address.
> + */
> mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
> }
I'm not any sort of expert on this code, but I don't see anything wrong.
Reviewed-by: Michael Ellerman <m...@ellerman.id.au>
cheers
