[PATCH 0/2] x86: Retry to remove vmalloc/ioremap synchronzation

[PATCH 0/2] x86: Retry to remove vmalloc/ioremap synchronzation

[Joerg Roedel]

From: Joerg Roedel <jroedel@suse.de>

Hi,

as discussed here are the updates to the recent patches and fixes to
pre-allocate the vmalloc/ioremap second-level page-table pages on
x86-64.

Patch one is a re-send of

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

with more explanations about what broke, what fixed it and why its now
safe to apply it again.

Patch two updates the comment in preallocate_vmalloc_pages(), it is
mostly the wording from Dave Hansen, so he really deserved the
authorship of it. I just didn't want to commit/send it in his name.
Feel free to change authorship of this patch to him.

Regards,

	Joerg

Joerg Roedel (2):
  x86/mm/64: Do not sync vmalloc/ioremap mappings
  x86/mm/64: Update comment in preallocate_vmalloc_pages()

 arch/x86/include/asm/pgtable_64_types.h |  2 --
 arch/x86/mm/init_64.c                   | 20 ++++++++++----------
 2 files changed, 10 insertions(+), 12 deletions(-)

-- 
2.28.0

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

[Joerg Roedel]

From: Joerg Roedel <jroedel@suse.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@suse.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

[tip: x86/mm] x86/mm/64: Do not sync vmalloc/ioremap mappings

[tip-bot2 for Joerg Roedel]

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     58a18fe95e83b8396605154db04d73b08063f31b
Gitweb:        https://git.kernel.org/tip/58a18fe95e83b8396605154db04d73b08063f31b
Author:        Joerg Roedel <jroedel@suse.de>
AuthorDate:    Fri, 14 Aug 2020 17:19:46 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sat, 15 Aug 2020 13:56:16 +02:00

x86/mm/64: Do not sync vmalloc/ioremap mappings

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@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200814151947.26229-2-joro@8bytes.org
---
 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 8f63efb..52e5f5f 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 a4ac13c..777d835 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.

[PATCH 2/2] x86/mm/64: Update comment in preallocate_vmalloc_pages()

[Joerg Roedel]

From: Joerg Roedel <jroedel@suse.de>

The comment explaining why 4-level systems only need to allocate on
the P4D level caused some confustion. Update it to better explain why
on 4-level systems the allocation on PUD level is necessary.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
---
 arch/x86/mm/init_64.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 777d83546764..124e63795ac9 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1252,14 +1252,19 @@ static void __init preallocate_vmalloc_pages(void)
 		if (!p4d)
 			goto failed;
 
-		/*
-		 * With 5-level paging the P4D level is not folded. So the PGDs
-		 * are now populated and there is no need to walk down to the
-		 * PUD level.
-		 */
 		if (pgtable_l5_enabled())
 			continue;
 
+		/*
+		 * The goal here is to allocate all possibly required
+		 * hardware page tables pointed to by the top hardware
+		 * level.
+		 *
+		 * On 4-level systems, the p4d layer is folded away and
+		 * the above code does no preallocation.  Below, go down
+		 * to the pud _software_ level to ensure the second
+		 * hardware level is allocated on 4-level systems too.
+		 */
 		lvl = "pud";
 		pud = pud_alloc(&init_mm, p4d, addr);
 		if (!pud)
-- 
2.28.0

[tip: x86/mm] x86/mm/64: Update comment in preallocate_vmalloc_pages()

[tip-bot2 for Joerg Roedel]

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     7a27ef5e83089090f3a4073a9157c862ef00acfc
Gitweb:        https://git.kernel.org/tip/7a27ef5e83089090f3a4073a9157c862ef00acfc
Author:        Joerg Roedel <jroedel@suse.de>
AuthorDate:    Fri, 14 Aug 2020 17:19:47 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sat, 15 Aug 2020 13:56:16 +02:00

x86/mm/64: Update comment in preallocate_vmalloc_pages()

The comment explaining why 4-level systems only need to allocate on
the P4D level caused some confustion. Update it to better explain why
on 4-level systems the allocation on PUD level is necessary.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200814151947.26229-3-joro@8bytes.org
---
 arch/x86/mm/init_64.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 777d835..b5a3fa4 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1252,14 +1252,19 @@ static void __init preallocate_vmalloc_pages(void)
 		if (!p4d)
 			goto failed;
 
-		/*
-		 * With 5-level paging the P4D level is not folded. So the PGDs
-		 * are now populated and there is no need to walk down to the
-		 * PUD level.
-		 */
 		if (pgtable_l5_enabled())
 			continue;
 
+		/*
+		 * The goal here is to allocate all possibly required
+		 * hardware page tables pointed to by the top hardware
+		 * level.
+		 *
+		 * On 4-level systems, the P4D layer is folded away and
+		 * the above code does no preallocation.  Below, go down
+		 * to the pud _software_ level to ensure the second
+		 * hardware level is allocated on 4-level systems too.
+		 */
 		lvl = "pud";
 		pud = pud_alloc(&init_mm, p4d, addr);
 		if (!pud)