Re: [PATCHv2 2/3] arm64: Add support for ARCH_SUPPORTS_DEBUG_PAGEALLOC

[Mark Rutland]

Hi,

On Fri, Jan 29, 2016 at 03:46:57PM -0800, Laura Abbott wrote:
> 
> ARCH_SUPPORTS_DEBUG_PAGEALLOC provides a hook to map and unmap
> pages for debugging purposes. This requires memory be mapped
> with PAGE_SIZE mappings since breaking down larger mappings
> at runtime will lead to TLB conflicts. Check if debug_pagealloc
> is enabled at runtime and if so, map everyting with PAGE_SIZE
> pages. Implement the functions to actually map/unmap the
> pages at runtime.
> 
> 
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>

I tried to apply atop of the arm64 for-next/pgtable branch, but git
wasn't very happy about that -- which branch/patches is this based on?

I'm not sure if I'm missing something, have something I shouldn't, or if
my MTA is corrupting patches again...

> ---
>  arch/arm64/Kconfig       |  3 +++
>  arch/arm64/mm/mmu.c      | 10 +++++++---
>  arch/arm64/mm/pageattr.c | 40 +++++++++++++++++++++++++++++++++-------
>  3 files changed, 43 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 8cc6228..0f33218 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -537,6 +537,9 @@ config HOTPLUG_CPU
>  source kernel/Kconfig.preempt
>  source kernel/Kconfig.hz
>  
> +config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> +	def_bool y
> +
>  config ARCH_HAS_HOLES_MEMORYMODEL
>  	def_bool y if SPARSEMEM
>  
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 103ebc0..5abbd30 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -181,7 +181,8 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
>  	do {
>  		next = pmd_addr_end(addr, end);
>  		/* try section mapping first */
> -		if (((addr | next | phys) & ~SECTION_MASK) == 0) {
> +		if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
> +		      (!debug_pagealloc_enabled() || !pgtable_alloc)) {
>  			pmd_t old_pmd =*pmd;
>  			set_pmd(pmd, __pmd(phys |
>  					   pgprot_val(mk_sect_prot(prot))));
> @@ -208,8 +209,11 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr, unsigned long end,
>  }
>  
>  static inline bool use_1G_block(unsigned long addr, unsigned long next,
> -			unsigned long phys)
> +			unsigned long phys, phys_addr_t (*pgtable_alloc)(void))
>  {
> +	if (pgtable_alloc && debug_pagealloc_enabled())
> +		return false;
> +
>  	if (PAGE_SHIFT != 12)
>  		return false;
>  
> @@ -241,7 +245,7 @@ static void alloc_init_pud(pgd_t *pgd, unsigned long addr, unsigned long end,
>  		/*
>  		 * For 4K granule only, attempt to put down a 1GB block
>  		 */
> -		if (use_1G_block(addr, next, phys)) {
> +		if (use_1G_block(addr, next, phys, pgtable_alloc)) {
>  			pud_t old_pud = *pud;
>  			set_pud(pud, __pud(phys |
>  					   pgprot_val(mk_sect_prot(prot))));

The checks for pgtable_alloc is to allow create_mapping_noalloc to use
sections regardless, right?

I got a little confused by that initially, but that seems to make sense.

> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 1360a02..69a8a7d 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -38,7 +38,8 @@ static int change_page_range(pte_t *ptep, pgtable_t token, unsigned long addr,
>  }
>  
>  static int change_memory_common(unsigned long addr, int numpages,
> -				pgprot_t set_mask, pgprot_t clear_mask)
> +				pgprot_t set_mask, pgprot_t clear_mask,
> +				bool ignore_vma_check)
>  {
>  	unsigned long start = addr;
>  	unsigned long size = PAGE_SIZE*numpages;
> @@ -65,11 +66,14 @@ static int change_memory_common(unsigned long addr, int numpages,
>  	 *
>  	 * So check whether the [addr, addr + size) interval is entirely
>  	 * covered by precisely one VM area that has the VM_ALLOC flag set.
> +	 *
> +	 * The one exception to this is is we're forcing everything to be
> +	 * page mapped with DEBUG_PAGEALLOC
>  	 */
>  	area = find_vm_area((void *)addr);
> -	if (!area ||
> +	if (!ignore_vma_check && (!area ||
>  	    end > (unsigned long)area->addr + area->size ||
> -	    !(area->flags & VM_ALLOC))
> +	    !(area->flags & VM_ALLOC)))
>  		return -EINVAL;

Perhaps we could pull out everything but the VMA checks into a static
__change_memory_common. Then we can call that directly in
__kernel_map_pages, and don't need to pass a confusing boolean
parameter.

Otherwise, this looks good to me.

Mark.

>  
>  	data.set_mask = set_mask;
> @@ -86,21 +90,24 @@ int set_memory_ro(unsigned long addr, int numpages)
>  {
>  	return change_memory_common(addr, numpages,
>  					__pgprot(PTE_RDONLY),
> -					__pgprot(PTE_WRITE));
> +					__pgprot(PTE_WRITE),
> +					false);
>  }
>  
>  int set_memory_rw(unsigned long addr, int numpages)
>  {
>  	return change_memory_common(addr, numpages,
>  					__pgprot(PTE_WRITE),
> -					__pgprot(PTE_RDONLY));
> +					__pgprot(PTE_RDONLY),
> +					false);
>  }
>  
>  int set_memory_nx(unsigned long addr, int numpages)
>  {
>  	return change_memory_common(addr, numpages,
>  					__pgprot(PTE_PXN),
> -					__pgprot(0));
> +					__pgprot(0),
> +					false);
>  }
>  EXPORT_SYMBOL_GPL(set_memory_nx);
>  
> @@ -108,6 +115,25 @@ int set_memory_x(unsigned long addr, int numpages)
>  {
>  	return change_memory_common(addr, numpages,
>  					__pgprot(0),
> -					__pgprot(PTE_PXN));
> +					__pgprot(PTE_PXN),
> +					false);
>  }
>  EXPORT_SYMBOL_GPL(set_memory_x);
> +
> +#ifdef CONFIG_DEBUG_PAGEALLOC
> +void __kernel_map_pages(struct page *page, int numpages, int enable)
> +{
> +	unsigned long addr = (unsigned long) page_address(page);
> +
> +	if (enable)
> +		change_memory_common(addr, numpages,
> +					__pgprot(PTE_VALID),
> +					__pgprot(0),
> +					true);
> +	else
> +		change_memory_common(addr, numpages,
> +					__pgprot(0),
> +					__pgprot(PTE_VALID),
> +					true);
> +}
> +#endif
> -- 
> 2.5.0
>