[PATCH 2/2] xen/swiotlb: don't destroy contiguous region in all cases

[Juergen Gross <jgross@suse.com>]

In case xen_swiotlb_alloc_coherent() needed to create a contiguous
region only for other reason than the memory not being compliant with
the device's DMA mask, there is no reason why this contiguous region
should be destroyed by xen_swiotlb_free_coherent() later. Destroying
this region should be done only, if the memory of the region was
allocated with more stringent placement requirements than the memory
it did replace.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/include/asm/xen/swiotlb-xen.h |  5 +++--
 arch/x86/xen/mmu_pv.c                  | 18 ++++++++++++------
 drivers/xen/swiotlb-xen.c              | 11 +++++++----
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/arch/x86/include/asm/xen/swiotlb-xen.h b/arch/x86/include/asm/xen/swiotlb-xen.h
index abde0f44df57..a353f20c7e79 100644
--- a/arch/x86/include/asm/xen/swiotlb-xen.h
+++ b/arch/x86/include/asm/xen/swiotlb-xen.h
@@ -4,8 +4,9 @@
 
 int xen_swiotlb_fixup(void *buf, unsigned long nslabs);
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
-				unsigned int address_bits,
-				dma_addr_t *dma_handle);
+				 unsigned int address_bits,
+				 dma_addr_t *dma_handle,
+				 unsigned int *address_bits_in);
 void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order);
 
 #endif /* _ASM_X86_SWIOTLB_XEN_H */
diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 2c70cd35e72c..fb586238f7c4 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -2208,19 +2208,22 @@ void __init xen_init_mmu_ops(void)
 static unsigned long discontig_frames[1<<MAX_CONTIG_ORDER];
 
 #define VOID_PTE (mfn_pte(0, __pgprot(0)))
-static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
-				unsigned long *in_frames,
-				unsigned long *out_frames)
+static int xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
+			     unsigned long *in_frames,
+			     unsigned long *out_frames)
 {
 	int i;
+	u64 address_bits = 0;
 	struct multicall_space mcs;
 
 	xen_mc_batch();
 	for (i = 0; i < (1UL<<order); i++, vaddr += PAGE_SIZE) {
 		mcs = __xen_mc_entry(0);
 
-		if (in_frames)
+		if (in_frames) {
 			in_frames[i] = virt_to_mfn((void *)vaddr);
+			address_bits |= in_frames[i] << PAGE_SHIFT;
+		}
 
 		MULTI_update_va_mapping(mcs.mc, vaddr, VOID_PTE, 0);
 		__set_phys_to_machine(virt_to_pfn((void *)vaddr), INVALID_P2M_ENTRY);
@@ -2229,6 +2232,8 @@ static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
 			out_frames[i] = virt_to_pfn((void *)vaddr);
 	}
 	xen_mc_issue(0);
+
+	return fls64(address_bits);
 }
 
 /*
@@ -2321,7 +2326,8 @@ static int xen_exchange_memory(unsigned long extents_in, unsigned int order_in,
 
 int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
 				 unsigned int address_bits,
-				 dma_addr_t *dma_handle)
+				 dma_addr_t *dma_handle,
+				 unsigned int *address_bits_in)
 {
 	unsigned long *in_frames = discontig_frames, out_frame;
 	unsigned long  flags;
@@ -2336,7 +2342,7 @@ int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
 	spin_lock_irqsave(&xen_reservation_lock, flags);
 
 	/* 1. Zap current PTEs, remembering MFNs. */
-	xen_zap_pfn_range(vstart, order, in_frames, NULL);
+	*address_bits_in = xen_zap_pfn_range(vstart, order, in_frames, NULL);
 
 	/* 2. Get a new contiguous memory extent. */
 	out_frame = virt_to_pfn((void *)vstart);
diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 26c62e0d34e9..3f3724f53914 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -118,6 +118,7 @@ int xen_swiotlb_fixup(void *buf, unsigned long nslabs)
 	int rc;
 	unsigned int order = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT);
 	unsigned int i, dma_bits = order + PAGE_SHIFT;
+	unsigned int dummy;
 	dma_addr_t dma_handle;
 	phys_addr_t p = virt_to_phys(buf);
 
@@ -129,7 +130,7 @@ int xen_swiotlb_fixup(void *buf, unsigned long nslabs)
 		do {
 			rc = xen_create_contiguous_region(
 				p + (i << IO_TLB_SHIFT), order,
-				dma_bits, &dma_handle);
+				dma_bits, &dma_handle, &dummy);
 		} while (rc && dma_bits++ < MAX_DMA_BITS);
 		if (rc)
 			return rc;
@@ -144,6 +145,7 @@ xen_swiotlb_alloc_coherent(struct device *dev, size_t size,
 		dma_addr_t *dma_handle, gfp_t flags, unsigned long attrs)
 {
 	u64 dma_mask = dev->coherent_dma_mask;
+	unsigned int address_bits = fls64(dma_mask), address_bits_in;
 	int order = get_order(size);
 	phys_addr_t phys;
 	void *ret;
@@ -160,10 +162,11 @@ xen_swiotlb_alloc_coherent(struct device *dev, size_t size,
 	if (*dma_handle + size - 1 > dma_mask ||
 	    range_straddles_page_boundary(phys, size) ||
 	    range_requires_alignment(phys, size)) {
-		if (xen_create_contiguous_region(phys, order, fls64(dma_mask),
-				dma_handle) != 0)
+		if (xen_create_contiguous_region(phys, order, address_bits,
+						 dma_handle, &address_bits_in))
 			goto out_free_pages;
-		SetPageXenRemapped(virt_to_page(ret));
+		if (address_bits_in > address_bits)
+			SetPageXenRemapped(virt_to_page(ret));
 	}
 
 	memset(ret, 0, size);
-- 
2.43.0