[PATCH RFC v1 1/7] swiotlb: introduce the highmem swiotlb buffer

[Dongli Zhang]

Currently, the virtio driver is not able to use 4+ GB memory when the
swiotlb is enforced, e.g., when amd sev is involved.

Fortunately, the SWIOTLB_ANY flag has been introduced since
commit 8ba2ed1be90f ("swiotlb: add a SWIOTLB_ANY flag to lift the low
memory restriction") to allocate swiotlb buffer from high memory.

While the default swiotlb is 'io_tlb_default_mem', the extra
'io_tlb_high_mem' is introduced to allocate with SWIOTLB_ANY flag in the
future patches. E.g., the user may configure the extra highmem swiotlb
buffer via "swiotlb=327680,4194304" to allocate 8GB memory.

In the future, the driver will be able to decide to use whether
'io_tlb_default_mem' or 'io_tlb_high_mem'.

The highmem swiotlb is enabled by user if io_tlb_high_mem is set. It can
be actively used if swiotlb_high_active() returns true.

The kernel command line "swiotlb=32768,3145728,force" is to allocate 64MB
for default swiotlb, and 6GB for the extra highmem swiotlb.

Cc: Konrad Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
 include/linux/swiotlb.h |  2 ++
 kernel/dma/swiotlb.c    | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 7ed35dd3de6e..e67e605af2dd 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -109,6 +109,7 @@ struct io_tlb_mem {
 	} *slots;
 };
 extern struct io_tlb_mem io_tlb_default_mem;
+extern struct io_tlb_mem io_tlb_high_mem;
 
 static inline bool is_swiotlb_buffer(struct device *dev, phys_addr_t paddr)
 {
@@ -164,6 +165,7 @@ static inline void swiotlb_adjust_size(unsigned long size)
 }
 #endif /* CONFIG_SWIOTLB */
 
+extern bool swiotlb_high_active(void);
 extern void swiotlb_print_info(void);
 
 #ifdef CONFIG_DMA_RESTRICTED_POOL
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index cb50f8d38360..569bc30e7b7a 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -66,10 +66,12 @@ static bool swiotlb_force_bounce;
 static bool swiotlb_force_disable;
 
 struct io_tlb_mem io_tlb_default_mem;
+struct io_tlb_mem io_tlb_high_mem;
 
 phys_addr_t swiotlb_unencrypted_base;
 
 static unsigned long default_nslabs = IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
+static unsigned long high_nslabs;
 
 static int __init
 setup_io_tlb_npages(char *str)
@@ -81,6 +83,15 @@ setup_io_tlb_npages(char *str)
 	}
 	if (*str == ',')
 		++str;
+
+	if (isdigit(*str)) {
+		/* avoid tail segment of size < IO_TLB_SEGSIZE */
+		high_nslabs =
+			ALIGN(simple_strtoul(str, &str, 0), IO_TLB_SEGSIZE);
+	}
+	if (*str == ',')
+		++str;
+
 	if (!strcmp(str, "force"))
 		swiotlb_force_bounce = true;
 	else if (!strcmp(str, "noforce"))
@@ -90,6 +101,11 @@ setup_io_tlb_npages(char *str)
 }
 early_param("swiotlb", setup_io_tlb_npages);
 
+bool swiotlb_high_active(void)
+{
+	return high_nslabs && io_tlb_high_mem.nslabs;
+}
+
 unsigned int swiotlb_max_segment(void)
 {
 	if (!io_tlb_default_mem.nslabs)
-- 
2.17.1