[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH V4 00/13] x86/Hyper-V: Add Hyper-V Isolation VM support
On 9/2/2021 3:59 PM, Christoph Hellwig wrote: On Tue, Aug 31, 2021 at 05:16:19PM +0000, Michael Kelley wrote:As a quick overview, I think there are four places where the shared_gpa_boundary must be applied to adjust the guest physical address that is used. Each requires mapping a corresponding virtual address range. Here are the four places: 1) The so-called "monitor pages" that are a core communication mechanism between the guest and Hyper-V. These are two single pages, and the mapping is handled by calling memremap() for each of the two pages. See Patch 7 of Tianyu's series.Ah, interesting.3) The network driver send and receive buffers. vmap_phys_range() should work here.Actually it won't. The problem with these buffers is that they are physically non-contiguous allocations. We really have two sensible options: 1) use vmap_pfn as in the current series. But in that case I think we should get rid of the other mapping created by vmalloc. I though a bit about finding a way to apply the offset in vmalloc itself, but I think it would be too invasive to the normal fast path. So the other sub-option would be to allocate the pages manually (maybe even using high order allocations to reduce TLB pressure) and then remap them Agree. In such case, the map for memory below shared_gpa_boundary is not necessary. allocate_pages() is limited by MAX_ORDER and needs to be called repeatedly to get enough memory. 2) do away with the contiguous kernel mapping entirely. This means the simple memcpy calls become loops over kmap_local_pfn. As I just found out for the send side that would be pretty easy, but the receive side would be more work. We'd also need to check the performance implications. kmap_local_pfn() requires pfn with backing struct page and this doesn't work pfn above shared_gpa_boundary. 4) The swiotlb memory used for bounce buffers. vmap_phys_range() should work here as well.Or memremap if it works for 1. Now use vmap_pfn() and the hv map function is reused in the netvsc driver. Case #2 above does unusual mapping. The ring buffer consists of a ring buffer header page, followed by one or more pages that are the actual ring buffer. The pages making up the actual ring buffer are mapped twice in succession. For example, if the ring buffer has 4 pages (one header page and three ring buffer pages), the contiguous virtual mapping must cover these seven pages: 0, 1, 2, 3, 1, 2, 3. The duplicate contiguous mapping allows the code that is reading or writing the actual ring buffer to not be concerned about wrap-around because writing off the end of the ring buffer is automatically wrapped-around by the mapping. The amount of data read or written in one batch never exceeds the size of the ring buffer, and after a batch is read or written, the read or write indices are adjusted to put them back into the range of the first mapping of the actual ring buffer pages. So there's method to the madness, and the technique works pretty well. But this kind of mapping is not amenable to using vmap_phys_range().Hmm. Can you point me to where this is mapped? Especially for the classic non-isolated case where no vmap/vmalloc mapping is involved at all? This is done via vmap() in the hv_ringbuffer_init() 182/* Initialize the ring buffer. */ 183int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,184 struct page *pages, u32 page_cnt, u32 max_pkt_size) 185{ 186 int i; 187 struct page **pages_wraparound; 188 189 BUILD_BUG_ON((sizeof(struct hv_ring_buffer) != PAGE_SIZE)); 190 191 /*192 * First page holds struct hv_ring_buffer, do wraparound mapping for 193 * the rest. 194 */195 pages_wraparound = kcalloc(page_cnt * 2 - 1, sizeof(struct page *), 196 GFP_KERNEL); 197 if (!pages_wraparound) 198 return -ENOMEM; 199 /* prepare to wrap page array */ 200 pages_wraparound[0] = pages; 201 for (i = 0; i < 2 * (page_cnt - 1); i++) 202 pages_wraparound[i + 1] = &pages[i % (page_cnt - 1) + 1]; 203 /* map */ 204 ring_info->ring_buffer = (struct hv_ring_buffer *)205 vmap(pages_wraparound, page_cnt * 2 - 1, VM_MAP, PAGE_KERNEL); 206 207 kfree(pages_wraparound); 208 209 210 if (!ring_info->ring_buffer) 211 return -ENOMEM; 212 213 ring_info->ring_buffer->read_index = 214 ring_info->ring_buffer->write_index = 0;
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