[Xen-devel] [PATCH v1] xen/swiotlb: rework early repeat code

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Current repeat code is plain broken for the early=true case. Xen exchanges
all DMA (<4GB) pages that it can on the first xen_swiotlb_fixup() attempt.
All further attempts with a halved region will fail immediately because
all DMA pages already belong to Dom0.

Introduce contig_pages param for xen_swiotlb_fixup() to track the number
of pages that were made contiguous in MFN space and use the same bootmem
region while halving the memory requirements.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 drivers/xen/swiotlb-xen.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 5dcb06fe9667..d2aba804d06c 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -142,7 +142,8 @@ static int is_xen_swiotlb_buffer(dma_addr_t dma_addr)
 static int max_dma_bits = 32;
 
 static int
-xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
+xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs,
+                 unsigned long *contig_pages)
 {
        int i, rc;
        int dma_bits;
@@ -156,10 +157,13 @@ xen_swiotlb_fixup(void *buf, size_t size, unsigned long 
nslabs)
                int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);
 
                do {
+                       unsigned int order = get_order(slabs << IO_TLB_SHIFT);
                        rc = xen_create_contiguous_region(
                                p + (i << IO_TLB_SHIFT),
-                               get_order(slabs << IO_TLB_SHIFT),
+                               order,
                                dma_bits, &dma_handle);
+                       if (rc == 0)
+                               *contig_pages += 1 << order;
                } while (rc && dma_bits++ < max_dma_bits);
                if (rc)
                        return rc;
@@ -202,7 +206,7 @@ static const char *xen_swiotlb_error(enum xen_swiotlb_err 
err)
 }
 int __ref xen_swiotlb_init(int verbose, bool early)
 {
-       unsigned long bytes, order;
+       unsigned long bytes, order, contig_pages;
        int rc = -ENOMEM;
        enum xen_swiotlb_err m_ret = XEN_SWIOTLB_UNKNOWN;
        unsigned int repeat = 3;
@@ -244,13 +248,32 @@ int __ref xen_swiotlb_init(int verbose, bool early)
        /*
         * And replace that memory with pages under 4GB.
         */
+       contig_pages = 0;
        rc = xen_swiotlb_fixup(xen_io_tlb_start,
                               bytes,
-                              xen_io_tlb_nslabs);
+                              xen_io_tlb_nslabs,
+                              &contig_pages);
        if (rc) {
-               if (early)
+               if (early) {
+                       unsigned long orig_bytes = bytes;
+                       while (repeat-- > 0) {
+                               xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
+                                                     (xen_io_tlb_nslabs >> 1));
+                               pr_info("Lowering to %luMB\n",
+                                    (xen_io_tlb_nslabs << IO_TLB_SHIFT) >> 20);
+                               bytes = xen_set_nslabs(xen_io_tlb_nslabs);
+                               order = get_order(xen_io_tlb_nslabs << 
IO_TLB_SHIFT);
+                               xen_io_tlb_end = xen_io_tlb_start + bytes;
+                               if (contig_pages >= (1ul << order)) {
+                                       /* Enough pages were made contiguous */
+                                       memblock_free(__pa(xen_io_tlb_start + 
bytes),
+                                                    PAGE_ALIGN(orig_bytes - 
bytes));
+                                       goto fixup_done;
+                               }
+                       }
                        memblock_free(__pa(xen_io_tlb_start),
                                      PAGE_ALIGN(bytes));
+               }
                else {
                        free_pages((unsigned long)xen_io_tlb_start, order);
                        xen_io_tlb_start = NULL;
@@ -258,6 +281,7 @@ int __ref xen_swiotlb_init(int verbose, bool early)
                m_ret = XEN_SWIOTLB_EFIXUP;
                goto error;
        }
+fixup_done:
        start_dma_addr = xen_virt_to_bus(xen_io_tlb_start);
        if (early) {
                if (swiotlb_init_with_tbl(xen_io_tlb_start, xen_io_tlb_nslabs,
@@ -272,7 +296,7 @@ int __ref xen_swiotlb_init(int verbose, bool early)
 
        return rc;
 error:
-       if (repeat--) {
+       if (repeat-- > 0) {
                xen_io_tlb_nslabs = max(1024UL, /* Min is 2MB */
                                        (xen_io_tlb_nslabs >> 1));
                pr_info("Lowering to %luMB\n",
-- 
2.17.1


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