linux-kernel - [PATCH 1/2] x86/mm/64: Do not sync vmalloc/ioremap mappings

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Message-Id: <20200814151947.26229-2-joro@8bytes.org>
Date:   Fri, 14 Aug 2020 17:19:46 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     x86@...nel.org
Cc:     Ingo Molnar <mingo@...nel.org>, Mike Rapoport <rppt@...ux.ibm.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, hpa@...or.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jason@...c4.com, Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, kirill.shutemov@...el.com,
        Joerg Roedel <jroedel@...e.de>
Subject: [PATCH 1/2] x86/mm/64: Do not sync vmalloc/ioremap mappings

From: Joerg Roedel <jroedel@...e.de>

Remove the code to sync the vmalloc and ioremap ranges for x86-64. The
page-table pages are all pre-allocated so that synchronization is
no longer necessary.

This is a patch that already went into the kernel as:

	commit 8bb9bf242d1f ("x86/mm/64: Do not sync vmalloc/ioremap mappings")

But it had to be reverted later because it unveiled a bug from:

	commit 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD pages for vmalloc area")

The bug in that commit causes the P4D/PUD pages not to be correctly
allocated, making the synchronization still necessary. That issue got
fixed meanwhile upstream:

	commit 995909a4e22b ("x86/mm/64: Do not dereference non-present PGD entries")

With that fix it is safe again to remove the page-table synchronization
for vmalloc/ioremap ranges on x86-64.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/include/asm/pgtable_64_types.h | 2 --
 arch/x86/mm/init_64.c                   | 5 -----
 2 files changed, 7 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 8f63efb2a2cc..52e5f5f2240d 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -159,6 +159,4 @@ extern unsigned int ptrs_per_p4d;
 
 #define PGD_KERNEL_START	((PAGE_SIZE / 2) / sizeof(pgd_t))
 
-#define ARCH_PAGE_TABLE_SYNC_MASK	(pgtable_l5_enabled() ?	PGTBL_PGD_MODIFIED : PGTBL_P4D_MODIFIED)
-
 #endif /* _ASM_X86_PGTABLE_64_DEFS_H */
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index a4ac13cc3fdc..777d83546764 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -217,11 +217,6 @@ static void sync_global_pgds(unsigned long start, unsigned long end)
 		sync_global_pgds_l4(start, end);
 }
 
-void arch_sync_kernel_mappings(unsigned long start, unsigned long end)
-{
-	sync_global_pgds(start, end);
-}
-
 /*
  * NOTE: This function is marked __ref because it calls __init function
  * (alloc_bootmem_pages). It's safe to do it ONLY when after_bootmem == 0.
-- 
2.28.0