Date:   Thu, 30 Jun 2022 16:38:08 +0800
From:   Guanghui Feng <guanghuifeng@...ux.alibaba.com>
To:     baolin.wang@...ux.alibaba.com, catalin.marinas@....com,
        will@...nel.org, akpm@...ux-foundation.org, david@...hat.com,
        jianyong.wu@....com, james.morse@....com, quic_qiancai@...cinc.com,
        christophe.leroy@...roup.eu, jonathan@...ek.ca,
        mark.rutland@....com, thunder.leizhen@...wei.com,
        anshuman.khandual@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, rppt@...nel.org,
        geert+renesas@...der.be, ardb@...nel.org, linux-mm@...ck.org,
        yaohongbo@...ux.alibaba.com
Cc:     alikernel-developer@...ux.alibaba.com
Subject: [PATCH v2] arm64: mm: fix linear mapping mem access performance degradation

The arm64 can build 2M/1G block/sectiion mapping. When using DMA/DMA32 zone
(enable crashkernel, disable rodata full, disable kfence), the mem_map will
use non block/section mapping(for crashkernel requires to shrink the region
in page granularity). But it will degrade performance when doing larging
continuous mem access in kernel(memcpy/memmove, etc).

There are many changes and discussions:
commit 031495635b46 ("arm64: Do not defer reserve_crashkernel() for
platforms with no DMA memory zones")
commit 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into
mem_init()")
commit 2687275a5843 ("arm64: Force NO_BLOCK_MAPPINGS if crashkernel
reservation is required")

This patch changes mem_map to use block/section mapping with crashkernel.
Firstly, do block/section mapping(normally 2M or 1G) for all avail mem at
mem_map, reserve crashkernel memory. And then walking pagetable to split
block/section mapping to non block/section mapping(normally 4K) [[[only]]]
for crashkernel mem. So the linear mem mapping use block/section mapping
as more as possible. We will reduce the cpu dTLB miss conspicuously, and
accelerate mem access about 10-20% performance improvement.

I have tested it with pft(Page Fault Test) and fio, obtained great
performace improvement.

For fio test:
1.prepare ramdisk
  modprobe -r brd
  modprobe brd rd_nr=1 rd_size=67108864
  dmsetup remove_all
  wipefs -a --force /dev/ram0
  mkfs -t ext4 -E lazy_itable_init=0,lazy_journal_init=0 -q -F /dev/ram0
  mkdir -p /fs/ram0
  mount -t ext4 /dev/ram0 /fs/ram0

2.prepare fio paremeter in x.fio file:
[global]
bs=4k
ioengine=psync
iodepth=128
size=32G
direct=1
invalidate=1
group_reporting
thread=1
rw=read
directory=/fs/ram0
numjobs=1

[task_0]
cpus_allowed=16
stonewall=1

3.run testcase:
perf stat -e dTLB-load-misses fio x.fio

4.contrast
------------------------
			without patch		with patch
fio READ		aggrb=1493.2MB/s	aggrb=1775.3MB/s
dTLB-load-misses	1,818,320,693		438,729,774
time elapsed(s)		70.500326434		62.877316408
user(s)			15.926332000		15.684721000
sys(s)			54.211939000		47.046165000

5.conclusion
Using this patch will reduce dTLB misses and improve performace greatly.

Signed-off-by: Guanghui Feng <guanghuifeng@...ux.alibaba.com>
---
 arch/arm64/include/asm/mmu.h |   1 +
 arch/arm64/mm/init.c         |   8 +--
 arch/arm64/mm/mmu.c          | 163 ++++++++++++++++++++++++++++++-------------
 3 files changed, 116 insertions(+), 56 deletions(-)

diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index 48f8466..1a46b81 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -63,6 +63,7 @@ static inline bool arm64_kernel_unmapped_at_el0(void)
 extern void arm64_memblock_init(void);
 extern void paging_init(void);
 extern void bootmem_init(void);
+extern void map_crashkernel(void);
 extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);
 extern void init_mem_pgprot(void);
 extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 339ee84..241d27e 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -190,6 +190,7 @@ static void __init reserve_crashkernel(void)
 	crashk_res.start = crash_base;
 	crashk_res.end = crash_base + crash_size - 1;
 	insert_resource(&iomem_resource, &crashk_res);
+	map_crashkernel();
 }
 
 /*
@@ -388,10 +389,6 @@ void __init arm64_memblock_init(void)
 	}
 
 	early_init_fdt_scan_reserved_mem();
-
-	if (!IS_ENABLED(CONFIG_ZONE_DMA) && !IS_ENABLED(CONFIG_ZONE_DMA32))
-		reserve_crashkernel();
-
 	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;
 }
 
@@ -438,8 +435,7 @@ void __init bootmem_init(void)
 	 * request_standard_resources() depends on crashkernel's memory being
 	 * reserved, so do it here.
 	 */
-	if (IS_ENABLED(CONFIG_ZONE_DMA) || IS_ENABLED(CONFIG_ZONE_DMA32))
-		reserve_crashkernel();
+	reserve_crashkernel();
 
 	memblock_dump_all();
 }
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 626ec32..c832848 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -42,6 +42,7 @@
 #define NO_BLOCK_MAPPINGS	BIT(0)
 #define NO_CONT_MAPPINGS	BIT(1)
 #define NO_EXEC_MAPPINGS	BIT(2)	/* assumes FEAT_HPDS is not used */
+#define NO_SEC_REMAPPINGS	BIT(3)	/* rebuild with non block/sec mapping*/
 
 u64 idmap_t0sz = TCR_T0SZ(VA_BITS_MIN);
 u64 idmap_ptrs_per_pgd = PTRS_PER_PGD;
@@ -156,11 +157,12 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
 }
 
 static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,
-		     phys_addr_t phys, pgprot_t prot)
+		     phys_addr_t phys, pgprot_t prot, int flags)
 {
 	pte_t *ptep;
 
-	ptep = pte_set_fixmap_offset(pmdp, addr);
+	ptep = (flags & NO_SEC_REMAPPINGS) ? pte_offset_kernel(pmdp, addr) :
+		pte_set_fixmap_offset(pmdp, addr);
 	do {
 		pte_t old_pte = READ_ONCE(*ptep);
 
@@ -176,7 +178,8 @@ static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,
 		phys += PAGE_SIZE;
 	} while (ptep++, addr += PAGE_SIZE, addr != end);
 
-	pte_clear_fixmap();
+	if (!(flags & NO_SEC_REMAPPINGS))
+		pte_clear_fixmap();
 }
 
 static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
@@ -208,11 +211,12 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
 		next = pte_cont_addr_end(addr, end);
 
 		/* use a contiguous mapping if the range is suitably aligned */
-		if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
+		if (!(flags & NO_SEC_REMAPPINGS) &&
+		   (((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
 		    (flags & NO_CONT_MAPPINGS) == 0)
 			__prot = __pgprot(pgprot_val(prot) | PTE_CONT);
 
-		init_pte(pmdp, addr, next, phys, __prot);
+		init_pte(pmdp, addr, next, phys, __prot, flags);
 
 		phys += next - addr;
 	} while (addr = next, addr != end);
@@ -224,15 +228,44 @@ static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end,
 {
 	unsigned long next;
 	pmd_t *pmdp;
+	phys_addr_t map_offset;
+	pmdval_t pmdval;
 
-	pmdp = pmd_set_fixmap_offset(pudp, addr);
+	pmdp = (flags & NO_SEC_REMAPPINGS) ? pmd_offset(pudp, addr) :
+		pmd_set_fixmap_offset(pudp, addr);
 	do {
 		pmd_t old_pmd = READ_ONCE(*pmdp);
 
 		next = pmd_addr_end(addr, end);
 
-		/* try section mapping first */
-		if (((addr | next | phys) & ~PMD_MASK) == 0 &&
+		if (flags & NO_SEC_REMAPPINGS) {
+			if (!pmd_none(*pmdp) && pmd_sect(*pmdp)) {
+				phys_addr_t pte_phys = pgtable_alloc(PAGE_SHIFT);
+				pmd_clear(pmdp);
+				pmdval = PMD_TYPE_TABLE | PMD_TABLE_UXN;
+				if (flags & NO_EXEC_MAPPINGS)
+					pmdval |= PMD_TABLE_PXN;
+				__pmd_populate(pmdp, pte_phys, pmdval);
+				flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+
+				map_offset = addr - (addr & PMD_MASK);
+				if (map_offset)
+				    alloc_init_cont_pte(pmdp, addr & PMD_MASK, addr,
+							phys - map_offset, prot,
+							pgtable_alloc,
+							flags & (~NO_SEC_REMAPPINGS));
+
+				if (next < (addr & PMD_MASK) + PMD_SIZE)
+				    alloc_init_cont_pte(pmdp, next,
+						       (addr & PUD_MASK) + PUD_SIZE,
+						        next - addr + phys,
+							prot, pgtable_alloc,
+							flags & (~NO_SEC_REMAPPINGS));
+			}
+			alloc_init_cont_pte(pmdp, addr, next, phys, prot,
+					    pgtable_alloc, flags);
+		}/* try section mapping first */
+		else if (((addr | next | phys) & ~PMD_MASK) == 0 &&
 		    (flags & NO_BLOCK_MAPPINGS) == 0) {
 			pmd_set_huge(pmdp, phys, prot);
 
@@ -252,7 +285,8 @@ static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end,
 		phys += next - addr;
 	} while (pmdp++, addr = next, addr != end);
 
-	pmd_clear_fixmap();
+	if (!(flags & NO_SEC_REMAPPINGS))
+		pmd_clear_fixmap();
 }
 
 static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
@@ -286,7 +320,8 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
 		next = pmd_cont_addr_end(addr, end);
 
 		/* use a contiguous mapping if the range is suitably aligned */
-		if ((((addr | next | phys) & ~CONT_PMD_MASK) == 0) &&
+		if (!(flags & NO_SEC_REMAPPINGS) &&
+		   (((addr | next | phys) & ~CONT_PMD_MASK) == 0) &&
 		    (flags & NO_CONT_MAPPINGS) == 0)
 			__prot = __pgprot(pgprot_val(prot) | PTE_CONT);
 
@@ -301,7 +336,9 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
 			   phys_addr_t (*pgtable_alloc)(int),
 			   int flags)
 {
+	phys_addr_t map_offset;
 	unsigned long next;
+	pudval_t pudval;
 	pud_t *pudp;
 	p4d_t *p4dp = p4d_offset(pgdp, addr);
 	p4d_t p4d = READ_ONCE(*p4dp);
@@ -325,18 +362,48 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
 	 */
 	if (system_state != SYSTEM_BOOTING)
 		mutex_lock(&fixmap_lock);
-	pudp = pud_set_fixmap_offset(p4dp, addr);
+
+	pudp = (flags & NO_SEC_REMAPPINGS) ? pud_offset(p4dp, addr) :
+		pud_set_fixmap_offset(p4dp, addr);
 	do {
 		pud_t old_pud = READ_ONCE(*pudp);
-
 		next = pud_addr_end(addr, end);
 
+		if (flags & NO_SEC_REMAPPINGS) {
+			if (!pud_none(*pudp) && pud_sect(*pudp)) {
+				phys_addr_t pmd_phys = pgtable_alloc(PMD_SHIFT);
+				pud_clear(pudp);
+				pudval = PUD_TYPE_TABLE | PUD_TABLE_UXN;
+				if (flags & NO_EXEC_MAPPINGS)
+					pudval |= PUD_TABLE_PXN;
+
+				__pud_populate(pudp, pmd_phys, pudval);
+				flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
+
+				map_offset = addr - (addr & PUD_MASK);
+				if (map_offset)
+				    alloc_init_cont_pmd(pudp, addr & PUD_MASK,
+							addr, phys - map_offset,
+							prot, pgtable_alloc,
+							flags &	(~NO_SEC_REMAPPINGS));
+
+				if (next < (addr & PUD_MASK) + PUD_SIZE)
+				    alloc_init_cont_pmd(pudp, next,
+						       (addr & PUD_MASK) +
+							PUD_SIZE,
+							next - addr + phys,
+							prot, pgtable_alloc,
+							flags & (~NO_SEC_REMAPPINGS));
+			}
+			alloc_init_cont_pmd(pudp, addr, next, phys, prot,
+					    pgtable_alloc, flags);
+		}
 		/*
 		 * For 4K granule only, attempt to put down a 1GB block
 		 */
-		if (pud_sect_supported() &&
-		   ((addr | next | phys) & ~PUD_MASK) == 0 &&
-		    (flags & NO_BLOCK_MAPPINGS) == 0) {
+		else if (pud_sect_supported() &&
+			((addr | next | phys) & ~PUD_MASK) == 0 &&
+			(flags & NO_BLOCK_MAPPINGS) == 0) {
 			pud_set_huge(pudp, phys, prot);
 
 			/*
@@ -355,7 +422,8 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
 		phys += next - addr;
 	} while (pudp++, addr = next, addr != end);
 
-	pud_clear_fixmap();
+	if (!(flags & NO_SEC_REMAPPINGS))
+		pud_clear_fixmap();
 	if (system_state != SYSTEM_BOOTING)
 		mutex_unlock(&fixmap_lock);
 }
@@ -483,20 +551,39 @@ void __init mark_linear_text_alias_ro(void)
 			    PAGE_KERNEL_RO);
 }
 
-static bool crash_mem_map __initdata;
+#ifdef CONFIG_KEXEC_CORE
+static phys_addr_t __init early_crashkernel_pgtable_alloc(int shift)
+{
+	phys_addr_t phys;
+	void *ptr;
 
-static int __init enable_crash_mem_map(char *arg)
+	phys = memblock_phys_alloc_range(PAGE_SIZE, PAGE_SIZE, 0,
+					 MEMBLOCK_ALLOC_NOLEAKTRACE);
+	if (!phys)
+		panic("Failed to allocate page table page\n");
+
+	ptr = (void *)__phys_to_virt(phys);
+	memset(ptr, 0, PAGE_SIZE);
+	return phys;
+}
+
+void __init map_crashkernel(void)
 {
-	/*
-	 * Proper parameter parsing is done by reserve_crashkernel(). We only
-	 * need to know if the linear map has to avoid block mappings so that
-	 * the crashkernel reservations can be unmapped later.
-	 */
-	crash_mem_map = true;
+	if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE))
+	    return;
 
-	return 0;
+	if (!crashk_res.end)
+	    return;
+
+	__create_pgd_mapping(swapper_pg_dir, crashk_res.start,
+			     __phys_to_virt(crashk_res.start),
+			     crashk_res.end + 1 - crashk_res.start, PAGE_KERNEL,
+			     early_crashkernel_pgtable_alloc,
+			     NO_EXEC_MAPPINGS | NO_SEC_REMAPPINGS);
 }
-early_param("crashkernel", enable_crash_mem_map);
+#else
+void __init map_crashkernel(void) {}
+#endif
 
 static void __init map_mem(pgd_t *pgdp)
 {
@@ -527,17 +614,6 @@ static void __init map_mem(pgd_t *pgdp)
 	 */
 	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
 
-#ifdef CONFIG_KEXEC_CORE
-	if (crash_mem_map) {
-		if (IS_ENABLED(CONFIG_ZONE_DMA) ||
-		    IS_ENABLED(CONFIG_ZONE_DMA32))
-			flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
-		else if (crashk_res.end)
-			memblock_mark_nomap(crashk_res.start,
-			    resource_size(&crashk_res));
-	}
-#endif
-
 	/* map all the memory banks */
 	for_each_mem_range(i, &start, &end) {
 		if (start >= end)
@@ -570,19 +646,6 @@ static void __init map_mem(pgd_t *pgdp)
 	 * in page granularity and put back unused memory to buddy system
 	 * through /sys/kernel/kexec_crash_size interface.
 	 */
-#ifdef CONFIG_KEXEC_CORE
-	if (crash_mem_map &&
-	    !IS_ENABLED(CONFIG_ZONE_DMA) && !IS_ENABLED(CONFIG_ZONE_DMA32)) {
-		if (crashk_res.end) {
-			__map_memblock(pgdp, crashk_res.start,
-				       crashk_res.end + 1,
-				       PAGE_KERNEL,
-				       NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
-			memblock_clear_nomap(crashk_res.start,
-					     resource_size(&crashk_res));
-		}
-	}
-#endif
 }
 
 void mark_rodata_ro(void)
-- 
1.8.3.1

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