Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper

[Martin Schwidefsky <schwidefsky@de.ibm.com>]

On Thu, 15 Jun 2017 17:52:22 +0300
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:

> We need an atomic way to setup pmd page table entry, avoiding races with
> CPU setting dirty/accessed bits. This is required to implement
> pmdp_invalidate() that doesn't loose these bits.
> 
> On PAE we have to use cmpxchg8b as we cannot assume what is value of new pmd and
> setting it up half-by-half can expose broken corrupted entry to CPU.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> ---
>  arch/x86/include/asm/pgtable-3level.h | 18 ++++++++++++++++++
>  arch/x86/include/asm/pgtable.h        | 14 ++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index f5af95a0c6b8..a924fc6a96b9 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -1092,6 +1092,20 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
>  	clear_bit(_PAGE_BIT_RW, (unsigned long *)pmdp);
>  }
> 
> +#ifndef pmdp_establish
> +#define pmdp_establish pmdp_establish
> +static inline pmd_t pmdp_establish(pmd_t *pmdp, pmd_t pmd)
> +{
> +	if (IS_ENABLED(CONFIG_SMP)) {
> +		return xchg(pmdp, pmd);
> +	} else {
> +		pmd_t old = *pmdp;
> +		*pmdp = pmd;
> +		return old;
> +	}
> +}
> +#endif
> +
>  /*
>   * clone_pgd_range(pgd_t *dst, pgd_t *src, int count);
>   *

For the s390 version of the pmdp_establish function we need the mm to be able
to do the TLB flush correctly. Can we please add a "struct vm_area_struct *vma"
argument to pmdp_establish analog to pmdp_invalidate?

The s390 patch would then look like this:
--
From 4d4641249d5e826c21c522d149553e89d73fcd4f Mon Sep 17 00:00:00 2001
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Date: Mon, 19 Jun 2017 07:40:11 +0200
Subject: [PATCH] s390/mm: add pmdp_establish

Define the pmdp_establish function to replace a pmd entry with a new
one and return the old value.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
 arch/s390/include/asm/pgtable.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index bb59a0aa3249..dedeecd5455c 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1511,6 +1511,13 @@ static inline void pmdp_invalidate(struct vm_area_struct *vma,
 	pmdp_xchg_direct(vma->vm_mm, addr, pmdp, __pmd(_SEGMENT_ENTRY_EMPTY));
 }
 
+static inline pmd_t pmdp_establish(struct vm_area_struct *vma,
+				   pmd_t *pmdp, pmd_t pmd)
+{
+	return pmdp_xchg_direct(vma->vm_mm, addr, pmdp, pmd);
+}
+#define pmdp_establish pmdp_establish
+
 #define __HAVE_ARCH_PMDP_SET_WRPROTECT
 static inline void pmdp_set_wrprotect(struct mm_struct *mm,
 				      unsigned long addr, pmd_t *pmdp)
-- 
2.11.2


-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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