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swiotlb-xen: maintain slab count properly

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Generic swiotlb code makes sure to keep the slab count a multiple of the
number of slabs per segment. Yet even without checking whether any such
assumption is made elsewhere, it is easy to see that xen_swiotlb_fixup()
might alter unrelated memory when calling xen_create_contiguous_region()
for the last segment, when that's not a full one - the function acts on
full order-N regions, not individual pages.

Align the slab count suitably when halving it for a retry. Add a build
time check and a runtime one. Replace the no longer useful local
variable "slabs" by an "order" one calculated just once, outside of the
loop. Re-use "order" for calculating "dma_bits", and change the type of
the latter as well as the one of "i" while touching this anyway.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

Link: https://lore.kernel.org/r/dc054cb0-bec4-4db0-fc06-c9fc957b6e66@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Jan Beulich 2021-09-07 14:05:12 +02:00 committed by Juergen Gross
parent 4c092c5901
commit d9a688add3
1 changed files with 9 additions and 10 deletions
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19
drivers/xen/swiotlb-xen.c
View file

@ -106,27 +106,26 @@ static int is_xen_swiotlb_buffer(struct device *dev, dma_addr_t dma_addr)
static int xen_swiotlb_fixup(void *buf, unsigned long nslabs)
{
int i, rc;
int dma_bits;
int rc;
unsigned int order = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT);
unsigned int i, dma_bits = order + PAGE_SHIFT;
dma_addr_t dma_handle;
phys_addr_t p = virt_to_phys(buf);
dma_bits = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT) + PAGE_SHIFT;
BUILD_BUG_ON(IO_TLB_SEGSIZE & (IO_TLB_SEGSIZE - 1));
BUG_ON(nslabs % IO_TLB_SEGSIZE);
i = 0;
do {
int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);
do {
rc = xen_create_contiguous_region(
p + (i << IO_TLB_SHIFT),
get_order(slabs << IO_TLB_SHIFT),
p + (i << IO_TLB_SHIFT), order,
dma_bits, &dma_handle);
} while (rc && dma_bits++ < MAX_DMA_BITS);
if (rc)
return rc;
i += slabs;
i += IO_TLB_SEGSIZE;
} while (i < nslabs);
return 0;
}
@ -210,7 +209,7 @@ int __ref xen_swiotlb_init(void)
error:
if (repeat--) {
/* Min is 2MB */
nslabs = max(1024UL, (nslabs >> 1));
nslabs = max(1024UL, ALIGN(nslabs >> 1, IO_TLB_SEGSIZE));
bytes = nslabs << IO_TLB_SHIFT;
pr_info("Lowering to %luMB\n", bytes >> 20);
goto retry;
@ -245,7 +244,7 @@ void __init xen_swiotlb_init_early(void)
memblock_free(__pa(start), PAGE_ALIGN(bytes));
if (repeat--) {
/* Min is 2MB */
nslabs = max(1024UL, (nslabs >> 1));
nslabs = max(1024UL, ALIGN(nslabs >> 1, IO_TLB_SEGSIZE));
bytes = nslabs << IO_TLB_SHIFT;
pr_info("Lowering to %luMB\n", bytes >> 20);
goto retry;