Subject: [PATCH v2] powerpc/pseries/svm: Allocate SWIOTLB buffer anywhere in memory

From: Thiago Jung Bauermann <[email-masked]>
Date: Mon, 17 Aug 2020 18:46:58 -0300

POWER secure guests (i.e., guests which use the Protection Execution
Facility) need to use SWIOTLB to be able to do I/O with the hypervisor, but
they don't need the SWIOTLB memory to be in low addresses since the
hypervisor doesn't have any addressing limitation.

This solves a SWIOTLB initialization problem we are seeing in secure guests
with 128 GB of RAM: they are configured with 4 GB of crashkernel reserved
memory, which leaves no space for SWIOTLB in low addresses.

To do this, we use mostly the same code as swiotlb_init(), but allocate the
buffer using memblock_alloc() instead of memblock_alloc_low().

We also need to add swiotlb_set_no_iotlb_memory() in order to set the
no_iotlb_memory flag if initialization fails.

Signed-off-by: Thiago Jung Bauermann <[email-masked]>
---
 arch/powerpc/include/asm/svm.h       |  4 ++++
 arch/powerpc/mm/mem.c                |  6 +++++-
 arch/powerpc/platforms/pseries/svm.c | 27 +++++++++++++++++++++++++++
 include/linux/swiotlb.h              |  1 +
 kernel/dma/swiotlb.c                 |  5 +++++
 5 files changed, 42 insertions(+), 1 deletion(-)

Changes from v1:
- Open-code swiotlb_init() in arch-specific code, as suggested by
  Christoph.

diff --git a/arch/powerpc/include/asm/svm.h b/arch/powerpc/include/asm/svm.h
index 85580b30aba4..7546402d796a 100644
--- a/arch/powerpc/include/asm/svm.h
+++ b/arch/powerpc/include/asm/svm.h
@@ -15,6 +15,8 @@ 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)
 
@@ -25,6 +27,8 @@ 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/mm/mem.c b/arch/powerpc/mm/mem.c
index c2c11eb8dcfc..0f21bcb16405 100644
--- a/arch/powerpc/mm/mem.c
+++ b/arch/powerpc/mm/mem.c
@@ -50,6 +50,7 @@
 #include <asm/swiotlb.h>
 #include <asm/rtas.h>
 #include <asm/kasan.h>
+#include <asm/svm.h>
 
 #include <mm/mmu_decl.h>
 
@@ -290,7 +291,10 @@ void __init mem_init(void)
 	 * back to to-down.
 	 */
 	memblock_set_bottom_up(true);
-	swiotlb_init(0);
+	if (is_secure_guest())
+		svm_swiotlb_init();
+	else
+		swiotlb_init(0);
 #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 40c0637203d5..d592e663a8d6 100644
--- a/arch/powerpc/platforms/pseries/svm.c
+++ b/arch/powerpc/platforms/pseries/svm.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/mm.h>
+#include <linux/memblock.h>
 #include <asm/machdep.h>
 #include <asm/svm.h>
 #include <asm/swiotlb.h>
@@ -34,6 +35,32 @@ 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;
+
+	if (io_tlb_start)
+		memblock_free_early(io_tlb_start,
+				    PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
+	pr_warn("Cannot allocate SWIOTLB buffer");
+	swiotlb_set_no_iotlb_memory(true);
+}
+
 int set_memory_encrypted(unsigned long addr, int numpages)
 {
 	if (!PAGE_ALIGNED(addr))
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 046bb94bd4d6..991e9f13e663 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -35,6 +35,7 @@ extern unsigned long swiotlb_nr_tbl(void);
 unsigned long swiotlb_size_or_default(void);
 extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
 extern void __init swiotlb_update_mem_attributes(void);
+void __init swiotlb_set_no_iotlb_memory(bool value);
 
 /*
  * Enumeration for sync targets
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index c19379fabd20..ed2b8818ff67 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -132,6 +132,11 @@ early_param("swiotlb", setup_io_tlb_npages);
 
 static bool no_iotlb_memory;
 
+void __init swiotlb_set_no_iotlb_memory(bool value)
+{
+	no_iotlb_memory = value;
+}
+
 unsigned long swiotlb_nr_tbl(void)
 {
 	return unlikely(no_iotlb_memory) ? 0 : io_tlb_nslabs;