[PATCH v6 0/4] riscv: tlb flush improvements

[PATCH v6 0/4] riscv: tlb flush improvements

[Alexandre Ghiti]

This series optimizes the tlb flushes on riscv which used to simply
flush the whole tlb whatever the size of the range to flush or the size
of the stride.

Patch 3 introduces a threshold that is microarchitecture specific and
will very likely be modified by vendors, not sure though which mechanism
we'll use to do that (dt? alternatives? vendor initialization code?).

Next steps would be to implement:
- svinval extension as Mayuresh did here [1]
- BATCHED_UNMAP_TLB_FLUSH (I'll wait for arm64 patchset to land)
- MMU_GATHER_RCU_TABLE_FREE
- MMU_GATHER_MERGE_VMAS

Any other idea welcome.

[1] https://lore.kernel.org/linux-riscv/20230623123849.1425805-1-mchitale@ventanamicro.com/

Changes in v6:
- Remove ifdef SVNAPOT, as suggested by Samuel
- Fix usage of u16 which could overflow, as noted by Samuel
- Use cpu_online_mask, as suggested by Samuel
- Move static_branch_unlikely(&use_asid_allocator) test, as suggested by Samuel
- Add TB/RB from Prabhakar and Samuel, thanks guys!

Changes in v5:
- Fix commit message s/flush_tlb/tlb_flush thanks to Samuel
- Simplify NAPOT mapping stride size handling, as suggested by Samuel
- Add TB from Prabhakar
- Add RB from Samuel
- Remove TB/RB from patch 2 as it changed enough

Changes in v4:
- Correctly handle the stride size for a NAPOT hugepage, thanks to Aaron Durbin!
- Fix flush_tlb_kernel_range() which passed a wrong argument to __flush_tlb_range()
- Factorize code to handle asid/no asid flushes
- Fix kernel flush bug where I used to pass 0 instead of x0, big thanks to Samuel for finding that!

Changes in v3:
- Add RB from Andrew, thanks!
- Unwrap a few lines, as suggested by Andrew
- Introduce defines for -1 constants used in tlbflush.c, as suggested by Andrew and Conor
- Use huge_page_size() directly instead of using the shift, as suggested by Andrew
- Remove misleading comments as suggested by Conor

Changes in v2:
- Make static tlb_flush_all_threshold, we'll figure out later how to
  override this value on a vendor basis, as suggested by Conor and Palmer
- Fix nommu build, as reported by Conor

Alexandre Ghiti (4):
  riscv: Improve tlb_flush()
  riscv: Improve flush_tlb_range() for hugetlb pages
  riscv: Make __flush_tlb_range() loop over pte instead of flushing the
    whole tlb
  riscv: Improve flush_tlb_kernel_range()

 arch/riscv/include/asm/sbi.h      |   3 -
 arch/riscv/include/asm/tlb.h      |   8 +-
 arch/riscv/include/asm/tlbflush.h |  15 ++-
 arch/riscv/kernel/sbi.c           |  32 ++----
 arch/riscv/mm/tlbflush.c          | 181 +++++++++++++++++++-----------
 5 files changed, 144 insertions(+), 95 deletions(-)

-- 
2.39.2


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[PATCH v6 1/4] riscv: Improve tlb_flush()

[Alexandre Ghiti]

For now, tlb_flush() simply calls flush_tlb_mm() which results in a
flush of the whole TLB. So let's use mmu_gather fields to provide a more
fine-grained flush of the TLB.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> # On RZ/Five SMARC
---
 arch/riscv/include/asm/tlb.h      | 8 +++++++-
 arch/riscv/include/asm/tlbflush.h | 3 +++
 arch/riscv/mm/tlbflush.c          | 7 +++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/tlb.h b/arch/riscv/include/asm/tlb.h
index 120bcf2ed8a8..1eb5682b2af6 100644
--- a/arch/riscv/include/asm/tlb.h
+++ b/arch/riscv/include/asm/tlb.h
@@ -15,7 +15,13 @@ static void tlb_flush(struct mmu_gather *tlb);
 
 static inline void tlb_flush(struct mmu_gather *tlb)
 {
-	flush_tlb_mm(tlb->mm);
+#ifdef CONFIG_MMU
+	if (tlb->fullmm || tlb->need_flush_all)
+		flush_tlb_mm(tlb->mm);
+	else
+		flush_tlb_mm_range(tlb->mm, tlb->start, tlb->end,
+				   tlb_get_unmap_size(tlb));
+#endif
 }
 
 #endif /* _ASM_RISCV_TLB_H */
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index a09196f8de68..f5c4fb0ae642 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -32,6 +32,8 @@ static inline void local_flush_tlb_page(unsigned long addr)
 #if defined(CONFIG_SMP) && defined(CONFIG_MMU)
 void flush_tlb_all(void);
 void flush_tlb_mm(struct mm_struct *mm);
+void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
+			unsigned long end, unsigned int page_size);
 void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr);
 void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 		     unsigned long end);
@@ -52,6 +54,7 @@ static inline void flush_tlb_range(struct vm_area_struct *vma,
 }
 
 #define flush_tlb_mm(mm) flush_tlb_all()
+#define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
 #endif /* !CONFIG_SMP || !CONFIG_MMU */
 
 /* Flush a range of kernel pages */
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 77be59aadc73..fa03289853d8 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -132,6 +132,13 @@ void flush_tlb_mm(struct mm_struct *mm)
 	__flush_tlb_range(mm, 0, -1, PAGE_SIZE);
 }
 
+void flush_tlb_mm_range(struct mm_struct *mm,
+			unsigned long start, unsigned long end,
+			unsigned int page_size)
+{
+	__flush_tlb_range(mm, start, end - start, page_size);
+}
+
 void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
 {
 	__flush_tlb_range(vma->vm_mm, addr, PAGE_SIZE, PAGE_SIZE);
-- 
2.39.2


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[PATCH v6 2/4] riscv: Improve flush_tlb_range() for hugetlb pages

[Alexandre Ghiti]

flush_tlb_range() uses a fixed stride of PAGE_SIZE and in its current form,
when a hugetlb mapping needs to be flushed, flush_tlb_range() flushes the
whole tlb: so set a stride of the size of the hugetlb mapping in order to
only flush the hugetlb mapping. However, if the hugepage is a NAPOT region,
all PTEs that constitute this mapping must be invalidated, so the stride
size must actually be the size of the PTE.

Note that THPs are directly handled by flush_pmd_tlb_range().

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> # On RZ/Five SMARC
---
 arch/riscv/mm/tlbflush.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index fa03289853d8..b6d712a82306 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -3,6 +3,7 @@
 #include <linux/mm.h>
 #include <linux/smp.h>
 #include <linux/sched.h>
+#include <linux/hugetlb.h>
 #include <asm/sbi.h>
 #include <asm/mmu_context.h>
 
@@ -147,7 +148,33 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
 void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 		     unsigned long end)
 {
-	__flush_tlb_range(vma->vm_mm, start, end - start, PAGE_SIZE);
+	unsigned long stride_size;
+
+	if (!is_vm_hugetlb_page(vma)) {
+		stride_size = PAGE_SIZE;
+	} else {
+		stride_size = huge_page_size(hstate_vma(vma));
+
+		/*
+		 * As stated in the privileged specification, every PTE in a
+		 * NAPOT region must be invalidated, so reset the stride in that
+		 * case.
+		 */
+		if (has_svnapot()) {
+			if (stride_size >= PGDIR_SIZE)
+				stride_size = PGDIR_SIZE;
+			else if (stride_size >= P4D_SIZE)
+				stride_size = P4D_SIZE;
+			else if (stride_size >= PUD_SIZE)
+				stride_size = PUD_SIZE;
+			else if (stride_size >= PMD_SIZE)
+				stride_size = PMD_SIZE;
+			else
+				stride_size = PAGE_SIZE;
+		}
+	}
+
+	__flush_tlb_range(vma->vm_mm, start, end - start, stride_size);
 }
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
-- 
2.39.2


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[PATCH v6 3/4] riscv: Make __flush_tlb_range() loop over pte instead of flushing the whole tlb

[Alexandre Ghiti]

Currently, when the range to flush covers more than one page (a 4K page or
a hugepage), __flush_tlb_range() flushes the whole tlb. Flushing the whole
tlb comes with a greater cost than flushing a single entry so we should
flush single entries up to a certain threshold so that:
threshold * cost of flushing a single entry < cost of flushing the whole
tlb.

Co-developed-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> # On RZ/Five SMARC
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Samuel Holland <samuel.holland@sifive.com>
---
 arch/riscv/include/asm/sbi.h      |   3 -
 arch/riscv/include/asm/tlbflush.h |   3 +
 arch/riscv/kernel/sbi.c           |  32 +++------
 arch/riscv/mm/tlbflush.c          | 115 +++++++++++++++---------------
 4 files changed, 72 insertions(+), 81 deletions(-)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 12dfda6bb924..0892f4421bc4 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -280,9 +280,6 @@ void sbi_set_timer(uint64_t stime_value);
 void sbi_shutdown(void);
 void sbi_send_ipi(unsigned int cpu);
 int sbi_remote_fence_i(const struct cpumask *cpu_mask);
-int sbi_remote_sfence_vma(const struct cpumask *cpu_mask,
-			   unsigned long start,
-			   unsigned long size);
 
 int sbi_remote_sfence_vma_asid(const struct cpumask *cpu_mask,
 				unsigned long start,
diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index f5c4fb0ae642..170a49c531c6 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -11,6 +11,9 @@
 #include <asm/smp.h>
 #include <asm/errata_list.h>
 
+#define FLUSH_TLB_MAX_SIZE      ((unsigned long)-1)
+#define FLUSH_TLB_NO_ASID       ((unsigned long)-1)
+
 #ifdef CONFIG_MMU
 extern unsigned long asid_mask;
 
diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index c672c8ba9a2a..5a62ed1da453 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -11,6 +11,7 @@
 #include <linux/reboot.h>
 #include <asm/sbi.h>
 #include <asm/smp.h>
+#include <asm/tlbflush.h>
 
 /* default SBI version is 0.1 */
 unsigned long sbi_spec_version __ro_after_init = SBI_SPEC_VERSION_DEFAULT;
@@ -376,32 +377,15 @@ int sbi_remote_fence_i(const struct cpumask *cpu_mask)
 }
 EXPORT_SYMBOL(sbi_remote_fence_i);
 
-/**
- * sbi_remote_sfence_vma() - Execute SFENCE.VMA instructions on given remote
- *			     harts for the specified virtual address range.
- * @cpu_mask: A cpu mask containing all the target harts.
- * @start: Start of the virtual address
- * @size: Total size of the virtual address range.
- *
- * Return: 0 on success, appropriate linux error code otherwise.
- */
-int sbi_remote_sfence_vma(const struct cpumask *cpu_mask,
-			   unsigned long start,
-			   unsigned long size)
-{
-	return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA,
-			    cpu_mask, start, size, 0, 0);
-}
-EXPORT_SYMBOL(sbi_remote_sfence_vma);
-
 /**
  * sbi_remote_sfence_vma_asid() - Execute SFENCE.VMA instructions on given
- * remote harts for a virtual address range belonging to a specific ASID.
+ * remote harts for a virtual address range belonging to a specific ASID or not.
  *
  * @cpu_mask: A cpu mask containing all the target harts.
  * @start: Start of the virtual address
  * @size: Total size of the virtual address range.
- * @asid: The value of address space identifier (ASID).
+ * @asid: The value of address space identifier (ASID), or FLUSH_TLB_NO_ASID
+ * for flushing all address spaces.
  *
  * Return: 0 on success, appropriate linux error code otherwise.
  */
@@ -410,8 +394,12 @@ int sbi_remote_sfence_vma_asid(const struct cpumask *cpu_mask,
 				unsigned long size,
 				unsigned long asid)
 {
-	return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA_ASID,
-			    cpu_mask, start, size, asid, 0);
+	if (asid == FLUSH_TLB_NO_ASID)
+		return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA,
+				    cpu_mask, start, size, 0, 0);
+	else
+		return __sbi_rfence(SBI_EXT_RFENCE_REMOTE_SFENCE_VMA_ASID,
+				    cpu_mask, start, size, asid, 0);
 }
 EXPORT_SYMBOL(sbi_remote_sfence_vma_asid);
 
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index b6d712a82306..e46fefc70927 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -9,28 +9,50 @@
 
 static inline void local_flush_tlb_all_asid(unsigned long asid)
 {
-	__asm__ __volatile__ ("sfence.vma x0, %0"
-			:
-			: "r" (asid)
-			: "memory");
+	if (asid != FLUSH_TLB_NO_ASID)
+		__asm__ __volatile__ ("sfence.vma x0, %0"
+				:
+				: "r" (asid)
+				: "memory");
+	else
+		local_flush_tlb_all();
 }
 
 static inline void local_flush_tlb_page_asid(unsigned long addr,
 		unsigned long asid)
 {
-	__asm__ __volatile__ ("sfence.vma %0, %1"
-			:
-			: "r" (addr), "r" (asid)
-			: "memory");
+	if (asid != FLUSH_TLB_NO_ASID)
+		__asm__ __volatile__ ("sfence.vma %0, %1"
+				:
+				: "r" (addr), "r" (asid)
+				: "memory");
+	else
+		local_flush_tlb_page(addr);
 }
 
-static inline void local_flush_tlb_range(unsigned long start,
-		unsigned long size, unsigned long stride)
+/*
+ * Flush entire TLB if number of entries to be flushed is greater
+ * than the threshold below.
+ */
+static unsigned long tlb_flush_all_threshold __read_mostly = 64;
+
+static void local_flush_tlb_range_threshold_asid(unsigned long start,
+						 unsigned long size,
+						 unsigned long stride,
+						 unsigned long asid)
 {
-	if (size <= stride)
-		local_flush_tlb_page(start);
-	else
-		local_flush_tlb_all();
+	unsigned long nr_ptes_in_range = DIV_ROUND_UP(size, stride);
+	int i;
+
+	if (nr_ptes_in_range > tlb_flush_all_threshold) {
+		local_flush_tlb_all_asid(asid);
+		return;
+	}
+
+	for (i = 0; i < nr_ptes_in_range; ++i) {
+		local_flush_tlb_page_asid(start, asid);
+		start += stride;
+	}
 }
 
 static inline void local_flush_tlb_range_asid(unsigned long start,
@@ -38,8 +60,10 @@ static inline void local_flush_tlb_range_asid(unsigned long start,
 {
 	if (size <= stride)
 		local_flush_tlb_page_asid(start, asid);
-	else
+	else if (size == FLUSH_TLB_MAX_SIZE)
 		local_flush_tlb_all_asid(asid);
+	else
+		local_flush_tlb_range_threshold_asid(start, size, stride, asid);
 }
 
 static void __ipi_flush_tlb_all(void *info)
@@ -52,7 +76,7 @@ void flush_tlb_all(void)
 	if (riscv_use_ipi_for_rfence())
 		on_each_cpu(__ipi_flush_tlb_all, NULL, 1);
 	else
-		sbi_remote_sfence_vma(NULL, 0, -1);
+		sbi_remote_sfence_vma_asid(NULL, 0, FLUSH_TLB_MAX_SIZE, FLUSH_TLB_NO_ASID);
 }
 
 struct flush_tlb_range_data {
@@ -69,18 +93,12 @@ static void __ipi_flush_tlb_range_asid(void *info)
 	local_flush_tlb_range_asid(d->start, d->size, d->stride, d->asid);
 }
 
-static void __ipi_flush_tlb_range(void *info)
-{
-	struct flush_tlb_range_data *d = info;
-
-	local_flush_tlb_range(d->start, d->size, d->stride);
-}
-
 static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 			      unsigned long size, unsigned long stride)
 {
 	struct flush_tlb_range_data ftd;
 	struct cpumask *cmask = mm_cpumask(mm);
+	unsigned long asid = FLUSH_TLB_NO_ASID;
 	unsigned int cpuid;
 	bool broadcast;
 
@@ -90,39 +108,24 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 	cpuid = get_cpu();
 	/* check if the tlbflush needs to be sent to other CPUs */
 	broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
-	if (static_branch_unlikely(&use_asid_allocator)) {
-		unsigned long asid = atomic_long_read(&mm->context.id) & asid_mask;
-
-		if (broadcast) {
-			if (riscv_use_ipi_for_rfence()) {
-				ftd.asid = asid;
-				ftd.start = start;
-				ftd.size = size;
-				ftd.stride = stride;
-				on_each_cpu_mask(cmask,
-						 __ipi_flush_tlb_range_asid,
-						 &ftd, 1);
-			} else
-				sbi_remote_sfence_vma_asid(cmask,
-							   start, size, asid);
-		} else {
-			local_flush_tlb_range_asid(start, size, stride, asid);
-		}
+
+	if (static_branch_unlikely(&use_asid_allocator))
+		asid = atomic_long_read(&mm->context.id) & asid_mask;
+
+	if (broadcast) {
+		if (riscv_use_ipi_for_rfence()) {
+			ftd.asid = asid;
+			ftd.start = start;
+			ftd.size = size;
+			ftd.stride = stride;
+			on_each_cpu_mask(cmask,
+					 __ipi_flush_tlb_range_asid,
+					 &ftd, 1);
+		} else
+			sbi_remote_sfence_vma_asid(cmask,
+						   start, size, asid);
 	} else {
-		if (broadcast) {
-			if (riscv_use_ipi_for_rfence()) {
-				ftd.asid = 0;
-				ftd.start = start;
-				ftd.size = size;
-				ftd.stride = stride;
-				on_each_cpu_mask(cmask,
-						 __ipi_flush_tlb_range,
-						 &ftd, 1);
-			} else
-				sbi_remote_sfence_vma(cmask, start, size);
-		} else {
-			local_flush_tlb_range(start, size, stride);
-		}
+		local_flush_tlb_range_asid(start, size, stride, asid);
 	}
 
 	put_cpu();
@@ -130,7 +133,7 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 
 void flush_tlb_mm(struct mm_struct *mm)
 {
-	__flush_tlb_range(mm, 0, -1, PAGE_SIZE);
+	__flush_tlb_range(mm, 0, FLUSH_TLB_MAX_SIZE, PAGE_SIZE);
 }
 
 void flush_tlb_mm_range(struct mm_struct *mm,
-- 
2.39.2


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[PATCH v6 4/4] riscv: Improve flush_tlb_kernel_range()

[Alexandre Ghiti]

This function used to simply flush the whole tlb of all harts, be more
subtile and try to only flush the range.

The problem is that we can only use PAGE_SIZE as stride since we don't know
the size of the underlying mapping and then this function will be improved
only if the size of the region to flush is < threshold * PAGE_SIZE.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> # On RZ/Five SMARC
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Samuel Holland <samuel.holland@sifive.com>
---
 arch/riscv/include/asm/tlbflush.h | 11 +++++-----
 arch/riscv/mm/tlbflush.c          | 34 ++++++++++++++++++++++---------
 2 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
index 170a49c531c6..8f3418c5f172 100644
--- a/arch/riscv/include/asm/tlbflush.h
+++ b/arch/riscv/include/asm/tlbflush.h
@@ -40,6 +40,7 @@ void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
 void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr);
 void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 		     unsigned long end);
+void flush_tlb_kernel_range(unsigned long start, unsigned long end);
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
 void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
@@ -56,15 +57,15 @@ static inline void flush_tlb_range(struct vm_area_struct *vma,
 	local_flush_tlb_all();
 }
 
-#define flush_tlb_mm(mm) flush_tlb_all()
-#define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
-#endif /* !CONFIG_SMP || !CONFIG_MMU */
-
 /* Flush a range of kernel pages */
 static inline void flush_tlb_kernel_range(unsigned long start,
 	unsigned long end)
 {
-	flush_tlb_all();
+	local_flush_tlb_all();
 }
 
+#define flush_tlb_mm(mm) flush_tlb_all()
+#define flush_tlb_mm_range(mm, start, end, page_size) flush_tlb_all()
+#endif /* !CONFIG_SMP || !CONFIG_MMU */
+
 #endif /* _ASM_RISCV_TLBFLUSH_H */
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index e46fefc70927..e6659d7368b3 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -97,20 +97,27 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 			      unsigned long size, unsigned long stride)
 {
 	struct flush_tlb_range_data ftd;
-	struct cpumask *cmask = mm_cpumask(mm);
+	const struct cpumask *cmask;
 	unsigned long asid = FLUSH_TLB_NO_ASID;
-	unsigned int cpuid;
 	bool broadcast;
 
-	if (cpumask_empty(cmask))
-		return;
+	if (mm) {
+		unsigned int cpuid;
+
+		cmask = mm_cpumask(mm);
+		if (cpumask_empty(cmask))
+			return;
 
-	cpuid = get_cpu();
-	/* check if the tlbflush needs to be sent to other CPUs */
-	broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
+		cpuid = get_cpu();
+		/* check if the tlbflush needs to be sent to other CPUs */
+		broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
 
-	if (static_branch_unlikely(&use_asid_allocator))
-		asid = atomic_long_read(&mm->context.id) & asid_mask;
+		if (static_branch_unlikely(&use_asid_allocator))
+			asid = atomic_long_read(&mm->context.id) & asid_mask;
+	} else {
+		cmask = cpu_online_mask;
+		broadcast = true;
+	}
 
 	if (broadcast) {
 		if (riscv_use_ipi_for_rfence()) {
@@ -128,7 +135,8 @@ static void __flush_tlb_range(struct mm_struct *mm, unsigned long start,
 		local_flush_tlb_range_asid(start, size, stride, asid);
 	}
 
-	put_cpu();
+	if (mm)
+		put_cpu();
 }
 
 void flush_tlb_mm(struct mm_struct *mm)
@@ -179,6 +187,12 @@ void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
 
 	__flush_tlb_range(vma->vm_mm, start, end - start, stride_size);
 }
+
+void flush_tlb_kernel_range(unsigned long start, unsigned long end)
+{
+	__flush_tlb_range(NULL, start, end - start, PAGE_SIZE);
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
 			unsigned long end)
-- 
2.39.2


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Re: [PATCH v6 0/4] riscv: tlb flush improvements

[Nadav Amit]

> On Oct 30, 2023, at 3:30 PM, Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
> 
> +			on_each_cpu_mask(cmask,
> +					 __ipi_flush_tlb_range_asid,
> +					 &ftd, 1);
> 

Unrelated, but having fed on the stack might cause it to be unaligned to
the cacheline, which in x86 we have seen introduces some overhead.

Actually, it is best not to put it on the stack, if possible to reduce
cache traffic.


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Re: [PATCH v6 0/4] riscv: tlb flush improvements

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <palmer@rivosinc.com>:

On Mon, 30 Oct 2023 14:30:24 +0100 you wrote:
> This series optimizes the tlb flushes on riscv which used to simply
> flush the whole tlb whatever the size of the range to flush or the size
> of the stride.
> 
> Patch 3 introduces a threshold that is microarchitecture specific and
> will very likely be modified by vendors, not sure though which mechanism
> we'll use to do that (dt? alternatives? vendor initialization code?).
> 
> [...]

Here is the summary with links:
  - [v6,1/4] riscv: Improve tlb_flush()
    https://git.kernel.org/riscv/c/c5e9b2c2ae82
  - [v6,2/4] riscv: Improve flush_tlb_range() for hugetlb pages
    https://git.kernel.org/riscv/c/c962a6e74639
  - [v6,3/4] riscv: Make __flush_tlb_range() loop over pte instead of flushing the whole tlb
    https://git.kernel.org/riscv/c/9d4e8d5fa7db
  - [v6,4/4] riscv: Improve flush_tlb_kernel_range()
    https://git.kernel.org/riscv/c/5e22bfd520ea

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html



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Re: [PATCH v6 0/4] riscv: tlb flush improvements

[Palmer Dabbelt]

On Mon, 30 Oct 2023 07:01:48 PDT (-0700), nadav.amit@gmail.com wrote:
>
>> On Oct 30, 2023, at 3:30 PM, Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>> 
>> +			on_each_cpu_mask(cmask,
>> +					 __ipi_flush_tlb_range_asid,
>> +					 &ftd, 1);
>> 
>
> Unrelated, but having fed

Do you mean `ftd`?

If so I'm not all that convinced that's a problem: sure it's 4x`long`, 
so we pass it on the stack instead of registers, but otherwise we'd need 
another `on_each_cpu_mask()` callback to shim stuff through via 
registers.

> on the stack might cause it to be unaligned to
> the cacheline, which in x86 we have seen introduces some overhead.

We have 128-bit stack alignment on RISC-V, so the elements are at least 
aligned.  Since they're just being loaded up as scalars for the next 
function call I'm not sure the alignment is all that exciting here.

> Actually, it is best not to put it on the stack, if possible to reduce
> cache traffic.

Sorry if I'm just missing something, but I'm not convinced this is a 
measurable performance problem.

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Re: [PATCH v6 0/4] riscv: tlb flush improvements

[Nadav Amit]

> On Nov 7, 2023, at 9:00 AM, Palmer Dabbelt <palmer@dabbelt.com> wrote:
> 
> On Mon, 30 Oct 2023 07:01:48 PDT (-0700), nadav.amit@gmail.com wrote:
>> 
>>> On Oct 30, 2023, at 3:30 PM, Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>>> + on_each_cpu_mask(cmask,
>>> + __ipi_flush_tlb_range_asid,
>>> + &ftd, 1);
>> 
>> Unrelated, but having fed
> 
> Do you mean `ftd`?
> 
> If so I'm not all that convinced that's a problem: sure it's 4x`long`, so we pass it on the stack instead of registers, but otherwise we'd need another `on_each_cpu_mask()` callback to shim stuff through via registers.

I have no idea why you need to move stuff through the registers.

>> Actually, it is best not to put it on the stack, if possible to reduce
>> cache traffic.
> 
> Sorry if I'm just missing something, but I'm not convinced this is a measurable performance problem.

I am not going to try to convince you (I ran the numbers on x86 a long
time ago).

There is a cost of bouncing cache-lines (because multiple cores access
the stack), TLB-miss on remote cores (which is mostly avoidable if ftd
is global).

Having said that, the optimizations you added now and intend to add in
the next steps are definitely more important for performance.


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