migration/ram: Factor out populating pages readable in ram_block_populate_pages()
Let's factor out prefaulting/populating to make further changes easier to review and add a comment what we are actually expecting to happen. While at it, use the actual page size of the ramblock, which defaults to qemu_real_host_page_size for anonymous memory. Further, rename ram_block_populate_pages() to ram_block_populate_read() as well, to make it clearer what we are doing. In the future, we might want to use MADV_POPULATE_READ to speed up population. Reviewed-by: Peter Xu <peterx@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Juan Quintela <quintela@redhat.com>
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@ -1639,26 +1639,35 @@ out:
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return ret;
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return ret;
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}
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}
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static inline void populate_read_range(RAMBlock *block, ram_addr_t offset,
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ram_addr_t size)
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{
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/*
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* We read one byte of each page; this will preallocate page tables if
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* required and populate the shared zeropage on MAP_PRIVATE anonymous memory
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* where no page was populated yet. This might require adaption when
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* supporting other mappings, like shmem.
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*/
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for (; offset < size; offset += block->page_size) {
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char tmp = *((char *)block->host + offset);
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/* Don't optimize the read out */
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asm volatile("" : "+r" (tmp));
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}
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}
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/*
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/*
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* ram_block_populate_pages: populate memory in the RAM block by reading
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* ram_block_populate_read: preallocate page tables and populate pages in the
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* an integer from the beginning of each page.
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* RAM block by reading a byte of each page.
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*
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*
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* Since it's solely used for userfault_fd WP feature, here we just
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* Since it's solely used for userfault_fd WP feature, here we just
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* hardcode page size to qemu_real_host_page_size.
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* hardcode page size to qemu_real_host_page_size.
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*
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*
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* @block: RAM block to populate
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* @block: RAM block to populate
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*/
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*/
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static void ram_block_populate_pages(RAMBlock *block)
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static void ram_block_populate_read(RAMBlock *block)
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{
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{
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char *ptr = (char *) block->host;
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populate_read_range(block, 0, block->used_length);
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for (ram_addr_t offset = 0; offset < block->used_length;
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offset += qemu_real_host_page_size) {
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char tmp = *(ptr + offset);
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/* Don't optimize the read out */
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asm volatile("" : "+r" (tmp));
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}
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}
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}
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/*
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/*
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@ -1684,7 +1693,7 @@ void ram_write_tracking_prepare(void)
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* UFFDIO_WRITEPROTECT_MODE_WP mode setting would silently skip
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* UFFDIO_WRITEPROTECT_MODE_WP mode setting would silently skip
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* pages with pte_none() entries in page table.
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* pages with pte_none() entries in page table.
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*/
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*/
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ram_block_populate_pages(block);
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ram_block_populate_read(block);
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}
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}
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}
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}
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