Hi Michael,

On 3/4/22 10:12 AM, Michael Kelley (LINUX) wrote:

From: Christoph Hellwig <hch@lst.de> Sent: Tuesday, March 1, 2022 2:53 AM

quoted

Power SVM wants to allocate a swiotlb buffer that is not restricted to low memory for
the trusted hypervisor scheme.  Consolidate the support for this into the swiotlb_init
interface by adding a new flag.

Hyper-V Isolated VMs want to do the same thing of not restricting the swiotlb
buffer to low memory.  That's what Tianyu Lan's patch set[1] is proposing.
Hyper-V synthetic devices have no DMA addressing limitations, and the
likelihood of using a PCI pass-thru device with addressing limitations in an
Isolated VM seems vanishingly small.

So could use of the SWIOTLB_ANY flag be generalized?  Let Hyper-V init
code set the flag before swiotlb_init() is called.  Or provide a CONFIG
variable that Hyper-V Isolated VMs could set.

I used to send 64-bit swiotlb, while at that time people thought it was the same
as Restricted DMA patchset.

https://lore.kernel.org/all/20210203233709.19819-1-dongli.zhang@oracle.com/ (local)

However, I do not think Restricted DMA patchset is going to supports 64-bit (or
high memory) DMA. Is this what you are looking for?

Dongli Zhang

Michael

[1] https://urldefense.com/v3/__https://lore.kernel.org/lkml/20220209122302.213882-1-ltykernel@gmail.com/__;!!ACWV5N9M2RV99hQ!fUx4fMgdQIrqJDDy-pbv9xMeyHX0rC6iN8176LWjylI2_lsjy03gysm0-lAbV1Yb7_g$ 

quoted

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/powerpc/include/asm/svm.h       |  4 ----
 arch/powerpc/include/asm/swiotlb.h   |  1 +
 arch/powerpc/kernel/dma-swiotlb.c    |  1 +
 arch/powerpc/mm/mem.c                |  5 +----
 arch/powerpc/platforms/pseries/svm.c | 26 +-------------------------
 include/linux/swiotlb.h              |  1 +
 kernel/dma/swiotlb.c                 |  9 +++++++--
 7 files changed, 12 insertions(+), 35 deletions(-)

diff --git a/arch/powerpc/include/asm/svm.h b/arch/powerpc/include/asm/svm.h
index 7546402d796af..85580b30aba48 100644
--- a/arch/powerpc/include/asm/svm.h
+++ b/arch/powerpc/include/asm/svm.h

@@ -15,8 +15,6 @@ static inline bool is_secure_guest(void)
 	return mfmsr() & MSR_S;
 }

-void __init svm_swiotlb_init(void);
-
 void dtl_cache_ctor(void *addr);
 #define get_dtl_cache_ctor()	(is_secure_guest() ? dtl_cache_ctor : NULL)

@@ -27,8 +25,6 @@ static inline bool is_secure_guest(void)
 	return false;
 }

-static inline void svm_swiotlb_init(void) {}
-
 #define get_dtl_cache_ctor() NULL

 #endif /* CONFIG_PPC_SVM */

diff --git a/arch/powerpc/include/asm/swiotlb.h

b/arch/powerpc/include/asm/swiotlb.h
index 3c1a1cd161286..4203b5e0a88ed 100644

--- a/arch/powerpc/include/asm/swiotlb.h
+++ b/arch/powerpc/include/asm/swiotlb.h

@@ -9,6 +9,7 @@
 #include <linux/swiotlb.h>

 extern unsigned int ppc_swiotlb_enable;
+extern unsigned int ppc_swiotlb_flags;

 #ifdef CONFIG_SWIOTLB
 void swiotlb_detect_4g(void);

diff --git a/arch/powerpc/kernel/dma-swiotlb.c b/arch/powerpc/kernel/dma-

swiotlb.c
index fc7816126a401..ba256c37bcc0f 100644

--- a/arch/powerpc/kernel/dma-swiotlb.c
+++ b/arch/powerpc/kernel/dma-swiotlb.c

@@ -10,6 +10,7 @@
 #include <asm/swiotlb.h>

 unsigned int ppc_swiotlb_enable;
+unsigned int ppc_swiotlb_flags;

 void __init swiotlb_detect_4g(void)
 {

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c index

e1519e2edc656..a4d65418c30a9 100644

--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c

@@ -249,10 +249,7 @@ void __init mem_init(void)
 	 * back to to-down.
 	 */
 	memblock_set_bottom_up(true);
-	if (is_secure_guest())
-		svm_swiotlb_init();
-	else
-		swiotlb_init(ppc_swiotlb_enable, 0);
+	swiotlb_init(ppc_swiotlb_enable, ppc_swiotlb_flags);
 #endif

 	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE); diff --git

a/arch/powerpc/platforms/pseries/svm.c b/arch/powerpc/platforms/pseries/svm.c
index c5228f4969eb2..3b4045d508ec8 100644

--- a/arch/powerpc/platforms/pseries/svm.c
+++ b/arch/powerpc/platforms/pseries/svm.c

@@ -28,7 +28,7 @@ static int __init init_svm(void)
 	 * need to use the SWIOTLB buffer for DMA even if dma_capable() says
 	 * otherwise.
 	 */
-	swiotlb_force = SWIOTLB_FORCE;
+	ppc_swiotlb_flags |= SWIOTLB_ANY | SWIOTLB_FORCE;

 	/* Share the SWIOTLB buffer with the host. */
 	swiotlb_update_mem_attributes();

@@ -37,30 +37,6 @@ static int __init init_svm(void)  }  machine_early_initcall(pseries,

init_svm);

-/*
- * Initialize SWIOTLB. Essentially the same as swiotlb_init(), except that it
- * can allocate the buffer anywhere in memory. Since the hypervisor doesn't have
- * any addressing limitation, we don't need to allocate it in low addresses.
- */
-void __init svm_swiotlb_init(void)
-{
-	unsigned char *vstart;
-	unsigned long bytes, io_tlb_nslabs;
-
-	io_tlb_nslabs = (swiotlb_size_or_default() >> IO_TLB_SHIFT);
-	io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
-
-	bytes = io_tlb_nslabs << IO_TLB_SHIFT;
-
-	vstart = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
-	if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, false))
-		return;
-
-
-	memblock_free(vstart, PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
-	panic("SVM: Cannot allocate SWIOTLB buffer");
-}
-
 int set_memory_encrypted(unsigned long addr, int numpages)  {
 	if (!cc_platform_has(CC_ATTR_MEM_ENCRYPT))

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h index

dcecf953f7997..ee655f2e4d28b 100644

--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h

@@ -15,6 +15,7 @@ struct scatterlist;

 #define SWIOTLB_VERBOSE	(1 << 0) /* verbose initialization */
 #define SWIOTLB_FORCE	(1 << 1) /* force bounce buffering */
+#define SWIOTLB_ANY	(1 << 2) /* allow any memory for the buffer */

 /*
  * Maximum allowable number of contiguous slabs to map, diff --git

a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 1a40c71c4d51a..77cf73dc20a78
100644

--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c

@@ -275,8 +275,13 @@ void __init swiotlb_init(bool addressing_limit, unsigned int

flags)
 	if (swiotlb_force_disable)
 		return;

-	/* Get IO TLB memory from the low pages */
-	tlb = memblock_alloc_low(bytes, PAGE_SIZE);
+	/*
+	 * By default allocate the bonuce buffer memory from low memory.
+	 */
+	if (flags & SWIOTLB_ANY)
+		tlb = memblock_alloc(bytes, PAGE_SIZE);
+	else
+		tlb = memblock_alloc_low(bytes, PAGE_SIZE);
 	if (!tlb)
 		goto fail;
 	if (swiotlb_init_with_tbl(tlb, default_nslabs, flags))
--
2.30.2