[PATCH] tlb/hugetlb: Add framework to handle PGDIR_SIZE HugeTLB pages

[PATCH] tlb/hugetlb: Add framework to handle PGDIR_SIZE HugeTLB pages

[Anshuman Khandual]

Change tlb_remove_huge_tlb_entry() to accommodate larger PGDIR_SIZE HugeTLB
pages via adding a new helper tlb_flush_pgd_range(). While here also update
struct mmu_gather as required, that is add a new member cleared_pgds.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Will Deacon <will@kernel.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: linux-arch@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
This applies on v5.18-rc2, some earlier context could be found here

https://lore.kernel.org/all/20220406112124.GD2731@worktop.programming.kicks-ass.net/

 include/asm-generic/tlb.h | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
index eee6f7763a39..6eaf0080ef2d 100644
--- a/include/asm-generic/tlb.h
+++ b/include/asm-generic/tlb.h
@@ -282,6 +282,7 @@ struct mmu_gather {
 	unsigned int		cleared_pmds : 1;
 	unsigned int		cleared_puds : 1;
 	unsigned int		cleared_p4ds : 1;
+	unsigned int		cleared_pgds : 1;
 
 	/*
 	 * tracks VM_EXEC | VM_HUGETLB in tlb_start_vma
@@ -325,6 +326,7 @@ static inline void __tlb_reset_range(struct mmu_gather *tlb)
 	tlb->cleared_pmds = 0;
 	tlb->cleared_puds = 0;
 	tlb->cleared_p4ds = 0;
+	tlb->cleared_pgds = 0;
 	/*
 	 * Do not reset mmu_gather::vma_* fields here, we do not
 	 * call into tlb_start_vma() again to set them if there is an
@@ -420,7 +422,7 @@ static inline void tlb_flush_mmu_tlbonly(struct mmu_gather *tlb)
 	 * these bits.
 	 */
 	if (!(tlb->freed_tables || tlb->cleared_ptes || tlb->cleared_pmds ||
-	      tlb->cleared_puds || tlb->cleared_p4ds))
+	      tlb->cleared_puds || tlb->cleared_p4ds || tlb->cleared_pgds))
 		return;
 
 	tlb_flush(tlb);
@@ -472,6 +474,8 @@ static inline unsigned long tlb_get_unmap_shift(struct mmu_gather *tlb)
 		return PUD_SHIFT;
 	if (tlb->cleared_p4ds)
 		return P4D_SHIFT;
+	if (tlb->cleared_pgds)
+		return PGDIR_SHIFT;
 
 	return PAGE_SHIFT;
 }
@@ -545,6 +549,14 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb,
 	tlb->cleared_p4ds = 1;
 }
 
+static inline void tlb_flush_pgd_range(struct mmu_gather *tlb,
+				     unsigned long address, unsigned long size)
+{
+	__tlb_adjust_range(tlb, address, size);
+	tlb->cleared_pgds = 1;
+}
+
+
 #ifndef __tlb_remove_tlb_entry
 #define __tlb_remove_tlb_entry(tlb, ptep, address) do { } while (0)
 #endif
@@ -565,7 +577,9 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb,
 #define tlb_remove_huge_tlb_entry(h, tlb, ptep, address)	\
 	do {							\
 		unsigned long _sz = huge_page_size(h);		\
-		if (_sz >= P4D_SIZE)				\
+		if (_sz >= PGDIR_SIZE)				\
+			tlb_flush_pgd_range(tlb, address, _sz);	\
+		else if (_sz >= P4D_SIZE)			\
 			tlb_flush_p4d_range(tlb, address, _sz);	\
 		else if (_sz >= PUD_SIZE)			\
 			tlb_flush_pud_range(tlb, address, _sz);	\
-- 
2.20.1

Re: [PATCH] tlb/hugetlb: Add framework to handle PGDIR_SIZE HugeTLB pages

[Peter Zijlstra]

On Wed, Apr 13, 2022 at 03:37:14PM +0530, Anshuman Khandual wrote:
> Change tlb_remove_huge_tlb_entry() to accommodate larger PGDIR_SIZE HugeTLB
> pages via adding a new helper tlb_flush_pgd_range(). While here also update
> struct mmu_gather as required, that is add a new member cleared_pgds.

I'm assuming Power will use this? Perhaps best to include it in a series
that actually makes use of it.

Other than that, looks good.

Re: [PATCH] tlb/hugetlb: Add framework to handle PGDIR_SIZE HugeTLB pages

[Matthew Wilcox]

On Wed, Apr 13, 2022 at 03:37:14PM +0530, Anshuman Khandual wrote:
> Change tlb_remove_huge_tlb_entry() to accommodate larger PGDIR_SIZE HugeTLB
> pages via adding a new helper tlb_flush_pgd_range(). While here also update
> struct mmu_gather as required, that is add a new member cleared_pgds.

Is this just completionist junk, or are there really CPUs that support
PGDIR sized pages?  We already have support for p4d (512GB), even though
at least Intel don't support pages larger than 1GB.  I think the largest
size page I've heard of is 16GB on POWER.  PGDIR_SIZE would be 256TB on
x86 which just seems ludicrous to be talking about supporting.

> ---
> This applies on v5.18-rc2, some earlier context could be found here
> 
> https://lore.kernel.org/all/20220406112124.GD2731@worktop.programming.kicks-ass.net/

Read it, doesn't talk about any real users of this.