linux-kernel - [PATCH AUTOSEL 5.7 065/388] powerpc/book3s64/radix/tlb: Determine hugepage flush correctly

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Date:   Wed, 17 Jun 2020 21:02:42 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Bharata B Rao <bharata@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH AUTOSEL 5.7 065/388] powerpc/book3s64/radix/tlb: Determine hugepage flush correctly

From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>

[ Upstream commit 8f53f9c0f68ab2168f637494b9e24034899c1310 ]

With a 64K page size flush with start and end:

  (start, end) = (721f680d0000, 721f680e0000)

results in:

  (hstart, hend) = (721f68200000, 721f68000000)

ie. hstart is above hend, which indicates no huge page flush is
needed.

However the current logic incorrectly sets hflush = true in this case,
because hstart != hend.

That causes us to call __tlbie_va_range() passing hstart/hend, to do a
huge page flush even though we don't need to. __tlbie_va_range() will
skip the actual tlbie operation for start > end. But it will still end
up calling fixup_tlbie_va_range() and doing the TLB fixups in there,
which is harmless but unnecessary work.

Reported-by: Bharata B Rao <bharata@...ux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@...il.com>
[mpe: Drop else case, hflush is already false, flesh out change log]
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20200513030616.152288-1-aneesh.kumar@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 arch/powerpc/mm/book3s64/radix_tlb.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
index 758ade2c2b6e..b5cc9b23cf02 100644
--- a/arch/powerpc/mm/book3s64/radix_tlb.c
+++ b/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -884,9 +884,7 @@ static inline void __radix__flush_tlb_range(struct mm_struct *mm,
 		if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
 			hstart = (start + PMD_SIZE - 1) & PMD_MASK;
 			hend = end & PMD_MASK;
-			if (hstart == hend)
-				hflush = false;
-			else
+			if (hstart < hend)
 				hflush = true;
 		}
 
-- 
2.25.1