On 2/2/2022 4:12 PM, Christoph Hellwig wrote:
I think this interface is a little too hacky. In the end all the
non-trusted hypervisor schemes (including the per-device swiotlb one)
can allocate the memory from everywhere and want for force use of
swiotlb. I think we need some kind of proper interface for that instead
of setting all kinds of global variables.
Hi Christoph:
Thanks for your review. I draft the following patch to export a
interface swiotlb_set_alloc_from_low_pages(). Could you have a look
whether this looks good for you.
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index f6c3638255d5..2b4f92668bc7 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -39,6 +39,7 @@ enum swiotlb_force {
extern void swiotlb_init(int verbose);
int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
unsigned long swiotlb_size_or_default(void);
+void swiotlb_set_alloc_from_low_pages(bool low);
extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
extern int swiotlb_late_init_with_default_size(size_t default_size);
extern void __init swiotlb_update_mem_attributes(void);
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index f1e7ea160b43..62bf8b5cc3e4 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -73,6 +73,8 @@ enum swiotlb_force swiotlb_force;
struct io_tlb_mem io_tlb_default_mem;
+static bool swiotlb_alloc_from_low_pages = true;
+
phys_addr_t swiotlb_unencrypted_base;
/*
@@ -116,6 +118,11 @@ void swiotlb_set_max_segment(unsigned int val)
max_segment = rounddown(val, PAGE_SIZE);
}
+void swiotlb_set_alloc_from_low_pages(bool low)
+{
+ swiotlb_alloc_from_low_pages = low;
+}
+
unsigned long swiotlb_size_or_default(void)
{
return default_nslabs << IO_TLB_SHIFT;
@@ -284,8 +291,15 @@ swiotlb_init(int verbose)
if (swiotlb_force == SWIOTLB_NO_FORCE)
return;
- /* Get IO TLB memory from the low pages */
- tlb = memblock_alloc_low(bytes, PAGE_SIZE);
+ /*
+ * Get IO TLB memory from the low pages if
swiotlb_alloc_from_low_pages
+ * is set.
+ */
+ if (swiotlb_alloc_from_low_pages)
+ tlb = memblock_alloc_low(bytes, PAGE_SIZE);
+ else
+ tlb = memblock_alloc(bytes, PAGE_SIZE);
+
if (!tlb)
goto fail;
if (swiotlb_init_with_tbl(tlb, default_nslabs, verbose))
