[4/5] arm64: mmap: Allow for "high" 52-bit VA allocations

Commit Message

Steve Capper Aug. 29, 2018, 12:45 p.m. UTC

This patch alters arch_get_unmapped_area and
arch_get_unmapped_area_topdown such that mmap calls with an addr
parameter that lie above 48-bit VAs will receive a VA that lies within
the 52-bit VA space on systems that support it.

Signed-off-by: Steve Capper <[e-mail]>
---
 arch/arm64/mm/mmap.c | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

Comments

Catalin Marinas Sept. 21, 2018, 5:11 p.m. UTC | #1

Hi Steve,

On Wed, Aug 29, 2018 at 01:45:42PM +0100, Steve Capper wrote:
> This patch alters arch_get_unmapped_area and
> arch_get_unmapped_area_topdown such that mmap calls with an addr
> parameter that lie above 48-bit VAs will receive a VA that lies within
> the 52-bit VA space on systems that support it.

The changes here don't seem to be too extensive. Can we not change the
generic code with some default functions that don't change the
functionality?

On x86 they had this code for years, so they patched it for 56-bit
support but on arm I'd like to still use the generic code.

> diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> index b516e0bfdb71..827414b69866 100644
> --- a/arch/arm64/mm/mmap.c
> +++ b/arch/arm64/mm/mmap.c
> @@ -81,6 +81,15 @@ static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>  
>  extern unsigned long mmap_min_addr;
>  
> +static unsigned long get_end_address(unsigned long addr)
> +{
> +	if (IS_ENABLED(CONFIG_ARM64_TRY_52BIT_VA) &&
> +			(addr > DEFAULT_MAP_WINDOW))
> +		return TASK_SIZE;
> +	else
> +		return DEFAULT_MAP_WINDOW;
> +}

We could as well have a generic get_end_address() (or a better name that
resembles high_limit) that always returns TASK_SIZE. We'd override it
for arm64.

Patch

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index b516e0bfdb71..827414b69866 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -81,6 +81,15 @@  static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
 
 extern unsigned long mmap_min_addr;
 
+static unsigned long get_end_address(unsigned long addr)
+{
+	if (IS_ENABLED(CONFIG_ARM64_TRY_52BIT_VA) &&
+			(addr > DEFAULT_MAP_WINDOW))
+		return TASK_SIZE;
+	else
+		return DEFAULT_MAP_WINDOW;
+}
+
 unsigned long
 arch_get_unmapped_area(struct file *filp, unsigned long addr,
 		unsigned long len, unsigned long pgoff, unsigned long flags)
@@ -88,8 +97,9 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	struct mm_struct *mm = current->mm;
 	struct vm_area_struct *vma, *prev;
 	struct vm_unmapped_area_info info;
+	unsigned long end = get_end_address(addr);
 
-	if (len > TASK_SIZE - mmap_min_addr)
+	if (len > end - mmap_min_addr)
 		return -ENOMEM;
 
 	if (flags & MAP_FIXED)
@@ -98,7 +108,7 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	if (addr) {
 		addr = PAGE_ALIGN(addr);
 		vma = find_vma_prev(mm, addr, &prev);
-		if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+		if (end - len >= addr && addr >= mmap_min_addr &&
 		    (!vma || addr + len <= vm_start_gap(vma)) &&
 		    (!prev || addr >= vm_end_gap(prev)))
 			return addr;
@@ -107,7 +117,7 @@  arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.flags = 0;
 	info.length = len;
 	info.low_limit = mm->mmap_base;
-	info.high_limit = TASK_SIZE;
+	info.high_limit = end;
 	info.align_mask = 0;
 	return vm_unmapped_area(&info);
 }
@@ -121,9 +131,10 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	struct mm_struct *mm = current->mm;
 	unsigned long addr = addr0;
 	struct vm_unmapped_area_info info;
+	unsigned long end = get_end_address(addr);
 
 	/* requested length too big for entire address space */
-	if (len > TASK_SIZE - mmap_min_addr)
+	if (len > end - mmap_min_addr)
 		return -ENOMEM;
 
 	if (flags & MAP_FIXED)
@@ -133,7 +144,7 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	if (addr) {
 		addr = PAGE_ALIGN(addr);
 		vma = find_vma_prev(mm, addr, &prev);
-		if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
+		if (end - len >= addr && addr >= mmap_min_addr &&
 				(!vma || addr + len <= vm_start_gap(vma)) &&
 				(!prev || addr >= vm_end_gap(prev)))
 			return addr;
@@ -143,6 +154,9 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 	info.length = len;
 	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 	info.high_limit = mm->mmap_base;
+	if (IS_ENABLED(CONFIG_ARM64_TRY_52BIT_VA) && (addr > DEFAULT_MAP_WINDOW))
+		info.high_limit += TASK_SIZE - DEFAULT_MAP_WINDOW;
+
 	info.align_mask = 0;
 	addr = vm_unmapped_area(&info);
 
@@ -156,7 +170,7 @@  arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 		VM_BUG_ON(addr != -ENOMEM);
 		info.flags = 0;
 		info.low_limit = TASK_UNMAPPED_BASE;
-		info.high_limit = TASK_SIZE;
+		info.high_limit = end;
 		addr = vm_unmapped_area(&info);
 	}