Re: [PATCH] x86/mm/pat: Support splitting of virtual memory areas

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Nam Cao <namcao@linutronix.de> [240825 11:29]:
> When a virtual memory area (VMA) gets splitted, memtype_rbroot's entries
> are not updated. This causes confusion later on when the VMAs get
> un-mapped, because the address ranges of the splitted VMAs do not match the
> address range of the initial VMA.
> 
> For example, if user does:
> 
> 	fd = open("/some/pci/bar", O_RDWR);
> 	addr = mmap(0, 8192, PROT_READ, MAP_SHARED, fd, 0);
> 	mprotect(addr, 4096, PROT_READ | PROT_WRITE);
> 	munmap(p, 8192);
> 
> with the physical address starting from 0xfd000000, the range
> (0xfd000000-0xfd002000) would be tracked with the mmap() call.
> 
> After mprotect(), the initial range gets splitted into
> (0xfd000000-0xfd001000) and (0xfd001000-0xfd002000).
> 
> Then, at munmap(), the first range does not match any entry in
> memtype_rbroot, and a message is seen in dmesg:
> 
>     x86/PAT: test:177 freeing invalid memtype [mem 0xfd000000-0xfd000fff]
> 
> The second range still matches by accident, because matching only the end
> address is acceptable (to handle shrinking VMA, added by 2039e6acaf94
> (x86/mm/pat: Change free_memtype() to support shrinking case)).

Does this need a fixes tag?

> 
> Make sure VMA splitting is handled properly, by splitting the entries in
> memtype_rbroot.
> 
> Signed-off-by: Nam Cao <namcao@linutronix.de>
> ---
>  arch/x86/mm/pat/memtype.c          | 59 ++++++++++++++++++++++++++++++
>  arch/x86/mm/pat/memtype.h          |  3 ++
>  arch/x86/mm/pat/memtype_interval.c | 22 +++++++++++
>  include/linux/pgtable.h            |  6 +++
>  mm/mmap.c                          |  8 ++++
>  5 files changed, 98 insertions(+)
> 
> diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c
> index bdc2a240c2aa..b60019478a76 100644
> --- a/arch/x86/mm/pat/memtype.c
> +++ b/arch/x86/mm/pat/memtype.c
> @@ -935,6 +935,46 @@ static int reserve_pfn_range(u64 paddr, unsigned long size, pgprot_t *vma_prot,
>  	return 0;
>  }
>  
> +static int split_pfn_range(u64 start, u64 end, u64 addr)
> +{
> +	struct memtype *entry_new;
> +	int is_range_ram, ret;
> +
> +	if (!pat_enabled())
> +		return 0;
> +
> +	start = sanitize_phys(start);
> +	end = sanitize_phys(end - 1) + 1;
> +
> +	/* Low ISA region is not tracked, it is always mapped WB */
> +	if (x86_platform.is_untracked_pat_range(start, end))
> +		return 0;
> +
> +	is_range_ram = pat_pagerange_is_ram(start, end);
> +	if (is_range_ram == 1)
> +		return 0;
> +
> +	if (is_range_ram < 0)
> +		return -EINVAL;
> +
> +	entry_new = kmalloc(sizeof(*entry_new), GFP_KERNEL);
> +	if (!entry_new)
> +		return -ENOMEM;
> +
> +	spin_lock(&memtype_lock);
> +	ret = memtype_split(start, end, addr, entry_new);
> +	spin_unlock(&memtype_lock);
> +
> +	if (ret) {
> +		pr_err("x86/PAT: %s:%d splitting invalid memtype [mem %#010Lx-%#010Lx]\n",
> +			current->comm, current->pid, start, end - 1);
> +		kfree(entry_new);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Internal interface to free a range of physical memory.
>   * Frees non RAM regions only.
> @@ -1072,6 +1112,25 @@ int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
>  	return 0;
>  }
>  
> +int track_pfn_split(struct vm_area_struct *vma, unsigned long addr)
> +{
> +	unsigned long vma_size = vma->vm_end - vma->vm_start;
> +	resource_size_t start_paddr, split_paddr;
> +	int ret;
> +
> +	if (vma->vm_flags & VM_PAT) {
> +		ret = get_pat_info(vma, &start_paddr, NULL);
> +		if (ret)
> +			return ret;
> +
> +		split_paddr = start_paddr + addr - vma->vm_start;
> +
> +		return split_pfn_range(start_paddr, start_paddr + vma_size, split_paddr);
> +	}
> +
> +	return 0;
> +}
> +
>  void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot, pfn_t pfn)
>  {
>  	enum page_cache_mode pcm;
> diff --git a/arch/x86/mm/pat/memtype.h b/arch/x86/mm/pat/memtype.h
> index cacecdbceb55..e01dc2018ab6 100644
> --- a/arch/x86/mm/pat/memtype.h
> +++ b/arch/x86/mm/pat/memtype.h
> @@ -31,6 +31,7 @@ static inline char *cattr_name(enum page_cache_mode pcm)
>  #ifdef CONFIG_X86_PAT
>  extern int memtype_check_insert(struct memtype *entry_new,
>  				enum page_cache_mode *new_type);
> +extern int memtype_split(u64 start, u64 end, u64 addr, struct memtype *entry_new);

I think we are dropping unnecessary externs now.

>  extern struct memtype *memtype_erase(u64 start, u64 end);
>  extern struct memtype *memtype_lookup(u64 addr);
>  extern int memtype_copy_nth_element(struct memtype *entry_out, loff_t pos);
> @@ -38,6 +39,8 @@ extern int memtype_copy_nth_element(struct memtype *entry_out, loff_t pos);
>  static inline int memtype_check_insert(struct memtype *entry_new,
>  				       enum page_cache_mode *new_type)
>  { return 0; }
> +static inline int memtype_split(u64 start, u64 end, u64 addr, struct memtype *entry_new)
> +{ return 0; }
>  static inline struct memtype *memtype_erase(u64 start, u64 end)
>  { return NULL; }
>  static inline struct memtype *memtype_lookup(u64 addr)
> diff --git a/arch/x86/mm/pat/memtype_interval.c b/arch/x86/mm/pat/memtype_interval.c
> index 645613d59942..c75d9ee6b72f 100644
> --- a/arch/x86/mm/pat/memtype_interval.c
> +++ b/arch/x86/mm/pat/memtype_interval.c
> @@ -128,6 +128,28 @@ int memtype_check_insert(struct memtype *entry_new, enum page_cache_mode *ret_ty
>  	return 0;
>  }
>  
> +int memtype_split(u64 start, u64 end, u64 addr, struct memtype *entry_new)
> +{
> +	struct memtype *entry_old;
> +
> +	entry_old = memtype_match(start, end, MEMTYPE_EXACT_MATCH);
> +	if (!entry_old)
> +		return -EINVAL;
> +
> +	interval_remove(entry_old, &memtype_rbroot);
> +
> +	entry_new->start = addr;
> +	entry_new->end	 = entry_old->end;
> +	entry_new->type	 = entry_old->type;
> +
> +	entry_old->end = addr;
> +
> +	interval_insert(entry_old, &memtype_rbroot);
> +	interval_insert(entry_new, &memtype_rbroot);
> +
> +	return 0;
> +}
> +
>  struct memtype *memtype_erase(u64 start, u64 end)
>  {
>  	struct memtype *entry_old;
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index 2a6a3cccfc36..8bfc8d0f5dd2 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -1502,6 +1502,11 @@ static inline int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
>  	return 0;
>  }
>  
> +static inline int track_pfn_split(struct vm_area_struct *vma, unsigned long addr)
> +{
> +	return 0;
> +}
> +
>  /*
>   * track_pfn_insert is called when a _new_ single pfn is established
>   * by vmf_insert_pfn().
> @@ -1542,6 +1547,7 @@ static inline void untrack_pfn_clear(struct vm_area_struct *vma)
>  extern int track_pfn_remap(struct vm_area_struct *vma, pgprot_t *prot,
>  			   unsigned long pfn, unsigned long addr,
>  			   unsigned long size);
> +extern int track_pfn_split(struct vm_area_struct *vma, unsigned long addr);

Same extern comment here.

>  extern void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
>  			     pfn_t pfn);
>  extern int track_pfn_copy(struct vm_area_struct *vma);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index d0dfc85b209b..64067ddb8382 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2486,6 +2486,12 @@ static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  	if (err)
>  		goto out_free_mpol;
>  
> +	if (unlikely(vma->vm_flags & VM_PFNMAP)) {

It is also a bit odd that you check VM_PFNMAP() here, then call a
function to check another flag?

> +		err = track_pfn_split(vma, addr);
> +		if (err)
> +			goto out_vma_unlink;
> +	}
> +

I don't think the __split_vma() location is the best place to put this.
Can this be done through the vm_ops->may_split() that is called above?

This is arch independent code that now has an x86 specific check, and
I'd like to keep __split_vma() out of the flag checking.  The only error
after the vm_ops check is ENOMEM (without any extra GFP restrictions on
the allocations), you don't need the new vma, and use the same arguments
passed to vm_ops->may_split().


>  	if (new->vm_file)
>  		get_file(new->vm_file);
>  
> @@ -2515,6 +2521,8 @@ static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  		vma_next(vmi);
>  	return 0;
>  
> +out_vma_unlink:
> +	unlink_anon_vmas(vma);
>  out_free_mpol:
>  	mpol_put(vma_policy(new));
>  out_free_vmi:
> -- 
> 2.39.2
>