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Date: Fri, 9 Jun 2017 17:23:06 -0700
From: Laura Abbott <labbott@...hat.com>
To: Tycho Andersen <tycho@...ker.com>, linux-mm@...ck.org
Cc: Juerg Haefliger <juergh@...il.com>, kernel-hardening@...ts.openwall.com
Subject: Re: [RFC v4 3/3] xpfo: add support for hugepages

On 06/07/2017 02:16 PM, Tycho Andersen wrote:
> Based on an earlier draft by Marco Benatto.
> 
> Signed-off-by: Tycho Andersen <tycho@...ker.com>
> CC: Juerg Haefliger <juergh@...il.com>
> ---
>  arch/x86/include/asm/pgtable.h | 22 +++++++++++++++
>  arch/x86/mm/pageattr.c         | 21 +++------------
>  arch/x86/mm/xpfo.c             | 61 +++++++++++++++++++++++++++++++++++++++++-
>  include/linux/xpfo.h           |  1 +
>  mm/xpfo.c                      |  8 ++----
>  5 files changed, 88 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index f5af95a0c6b8..58bb43d8b9c1 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -1185,6 +1185,28 @@ static inline u16 pte_flags_pkey(unsigned long pte_flags)
>  #endif
>  }
>  
> +/*
> + * The current flushing context - we pass it instead of 5 arguments:
> + */
> +struct cpa_data {
> +	unsigned long	*vaddr;
> +	pgd_t		*pgd;
> +	pgprot_t	mask_set;
> +	pgprot_t	mask_clr;
> +	unsigned long	numpages;
> +	int		flags;
> +	unsigned long	pfn;
> +	unsigned	force_split : 1;
> +	int		curpage;
> +	struct page	**pages;
> +};
> +
> +int
> +try_preserve_large_page(pte_t *kpte, unsigned long address,
> +			struct cpa_data *cpa);
> +int split_large_page(struct cpa_data *cpa, pte_t *kpte,
> +		     unsigned long address);
> +
>  #include <asm-generic/pgtable.h>
>  #endif	/* __ASSEMBLY__ */
>  
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 1dcd2be4cce4..6d6a78e6e023 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -26,21 +26,6 @@
>  #include <asm/pat.h>
>  #include <asm/set_memory.h>
>  
> -/*
> - * The current flushing context - we pass it instead of 5 arguments:
> - */
> -struct cpa_data {
> -	unsigned long	*vaddr;
> -	pgd_t		*pgd;
> -	pgprot_t	mask_set;
> -	pgprot_t	mask_clr;
> -	unsigned long	numpages;
> -	int		flags;
> -	unsigned long	pfn;
> -	unsigned	force_split : 1;
> -	int		curpage;
> -	struct page	**pages;
> -};
>  
>  /*
>   * Serialize cpa() (for !DEBUG_PAGEALLOC which uses large identity mappings)
> @@ -506,7 +491,7 @@ static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte)
>  #endif
>  }
>  
> -static int
> +int
>  try_preserve_large_page(pte_t *kpte, unsigned long address,
>  			struct cpa_data *cpa)
>  {
> @@ -740,8 +725,8 @@ __split_large_page(struct cpa_data *cpa, pte_t *kpte, unsigned long address,
>  	return 0;
>  }
>  
> -static int split_large_page(struct cpa_data *cpa, pte_t *kpte,
> -			    unsigned long address)
> +int split_large_page(struct cpa_data *cpa, pte_t *kpte,
> +		     unsigned long address)
>  {
>  	struct page *base;
>  
> diff --git a/arch/x86/mm/xpfo.c b/arch/x86/mm/xpfo.c
> index c24b06c9b4ab..818da3ebc077 100644
> --- a/arch/x86/mm/xpfo.c
> +++ b/arch/x86/mm/xpfo.c
> @@ -13,11 +13,70 @@
>  
>  #include <linux/mm.h>
>  
> +#include <asm/tlbflush.h>
> +
>  /* Update a single kernel page table entry */
>  inline void set_kpte(void *kaddr, struct page *page, pgprot_t prot)
>  {
>  	unsigned int level;
>  	pte_t *pte = lookup_address((unsigned long)kaddr, &level);
>  
> -	set_pte_atomic(pte, pfn_pte(page_to_pfn(page), canon_pgprot(prot)));
> +
> +	BUG_ON(!pte);
> +
> +	switch (level) {
> +	case PG_LEVEL_4K:
> +		set_pte_atomic(pte, pfn_pte(page_to_pfn(page), canon_pgprot(prot)));
> +		break;
> +	case PG_LEVEL_2M:
> +	case PG_LEVEL_1G: {
> +		struct cpa_data cpa;
> +		int do_split;
> +
> +		memset(&cpa, 0, sizeof(cpa));
> +		cpa.vaddr = kaddr;
> +		cpa.pages = &page;
> +		cpa.mask_set = prot;
> +		pgprot_val(cpa.mask_clr) = ~pgprot_val(prot);
> +		cpa.numpages = 1;
> +		cpa.flags = 0;
> +		cpa.curpage = 0;
> +		cpa.force_split = 0;
> +
> +		do_split = try_preserve_large_page(pte, (unsigned long)kaddr, &cpa);
> +		if (do_split < 0)

I can't reproduce the failure you describe in the cover letter but are you sure this
check is correct? It looks like try_preserve_large_page can return 1 on failure
and you still need to call split_large_page.

> +			BUG_ON(split_large_page(&cpa, pte, (unsigned long)kaddr));
> +
> +		break;
> +	}
> +	default:
> +		BUG();
> +	}
> +
> +}
> +
> +inline void xpfo_flush_kernel_page(struct page *page, int order)
> +{
> +	int level;
> +	unsigned long size, kaddr;
> +
> +	kaddr = (unsigned long)page_address(page);
> +	lookup_address(kaddr, &level);
> +
> +
> +	switch (level) {
> +	case PG_LEVEL_4K:
> +		size = PAGE_SIZE;
> +		break;
> +	case PG_LEVEL_2M:
> +		size = PMD_SIZE;
> +		break;
> +	case PG_LEVEL_1G:
> +		size = PUD_SIZE;
> +		break;
> +	default:
> +		BUG();
> +	}
> +
> +	flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size);
>  }
> diff --git a/include/linux/xpfo.h b/include/linux/xpfo.h
> index 031cbee22a41..a0f0101720f6 100644
> --- a/include/linux/xpfo.h
> +++ b/include/linux/xpfo.h
> @@ -19,6 +19,7 @@
>  extern struct page_ext_operations page_xpfo_ops;
>  
>  void set_kpte(void *kaddr, struct page *page, pgprot_t prot);
> +void xpfo_flush_kernel_page(struct page *page, int order);
>  
>  void xpfo_kmap(void *kaddr, struct page *page);
>  void xpfo_kunmap(void *kaddr, struct page *page);
> diff --git a/mm/xpfo.c b/mm/xpfo.c
> index 8384058136b1..895de28108da 100644
> --- a/mm/xpfo.c
> +++ b/mm/xpfo.c
> @@ -78,7 +78,6 @@ void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp)
>  {
>  	int i, flush_tlb = 0;
>  	struct xpfo *xpfo;
> -	unsigned long kaddr;
>  
>  	if (!static_branch_unlikely(&xpfo_inited))
>  		return;
> @@ -109,11 +108,8 @@ void xpfo_alloc_pages(struct page *page, int order, gfp_t gfp)
>  		}
>  	}
>  
> -	if (flush_tlb) {
> -		kaddr = (unsigned long)page_address(page);
> -		flush_tlb_kernel_range(kaddr, kaddr + (1 << order) *
> -				       PAGE_SIZE);
> -	}
> +	if (flush_tlb)
> +		xpfo_flush_kernel_page(page, order);
>  }
>  
>  void xpfo_free_pages(struct page *page, int order)
> 

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