linux-kernel - [PATCH] swiotlb: Allow allocating buffer anywhere in memory

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Date:   Sat, 15 Aug 2020 17:45:36 -0300
From:   Thiago Jung Bauermann <bauerman@...ux.ibm.com>
To:     iommu@...ts.linux-foundation.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Ram Pai <linuxram@...ibm.com>,
        Satheesh Rajendran <sathnaga@...ux.vnet.ibm.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Subject: [PATCH] swiotlb: Allow allocating buffer anywhere in memory

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.

Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
---
 arch/powerpc/mm/mem.c   |  7 ++++++-
 include/linux/swiotlb.h |  8 +++++++-
 kernel/dma/swiotlb.c    | 10 +++++++---
 3 files changed, 20 insertions(+), 5 deletions(-)

Normally I would split changes like this into one patch touching generic
code and another for the arch-specific part, but in this case I thought it
would be unneeded complexity. I can split though if people prefer it that
way.

diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
index c2c11eb8dcfc..13f2e3aff8b5 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 +291,11 @@ void __init mem_init(void)
 	 * back to to-down.
 	 */
 	memblock_set_bottom_up(true);
-	swiotlb_init(0);
+	/*
+	 * SVM guests can use the SWIOTLB wherever it is in memory,
+	 * even if not DMA-able.
+	 */
+	swiotlb_init_anywhere(0, is_secure_guest());
 #endif
 
 	high_memory = (void *) __va(max_low_pfn * PAGE_SIZE);
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 046bb94bd4d6..433f3dbb35b5 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -29,7 +29,13 @@ enum swiotlb_force {
  */
 #define IO_TLB_SHIFT 11
 
-extern void swiotlb_init(int verbose);
+void __init swiotlb_init_anywhere(int verbose, bool allocate_anywhere);
+
+static inline void swiotlb_init(int verbose)
+{
+	swiotlb_init_anywhere(verbose, false);
+}
+
 int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
 extern unsigned long swiotlb_nr_tbl(void);
 unsigned long swiotlb_size_or_default(void);
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index c19379fabd20..27070aa59e34 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -244,7 +244,7 @@ int __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
  * structures for the software IO TLB used to implement the DMA API.
  */
 void  __init
-swiotlb_init(int verbose)
+swiotlb_init_anywhere(int verbose, bool allocate_anywhere)
 {
 	size_t default_size = IO_TLB_DEFAULT_SIZE;
 	unsigned char *vstart;
@@ -257,8 +257,12 @@ swiotlb_init(int verbose)
 
 	bytes = io_tlb_nslabs << IO_TLB_SHIFT;
 
-	/* Get IO TLB memory from the low pages */
-	vstart = memblock_alloc_low(PAGE_ALIGN(bytes), PAGE_SIZE);
+	if (allocate_anywhere)
+		vstart = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
+	else
+		/* Get IO TLB memory from the low pages */
+		vstart = memblock_alloc_low(PAGE_ALIGN(bytes), PAGE_SIZE);
+
 	if (vstart && !swiotlb_init_with_tbl(vstart, io_tlb_nslabs, verbose))
 		return;