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Date: Tue, 4 Dec 2018 00:04:21 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
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<davem@...emloft.net>, "Keshavamurthy, Anil S"
<anil.s.keshavamurthy@...el.com>
Subject: Re: [PATCH 1/2] vmalloc: New flag for flush before releasing pages
It looks like this new flag is in linux-next now. As I am reading it, these
architectures have a module_alloc that uses some sort of executable flag and
are not using the default module_alloc which is already covered, and so may need
it plugged in:
arm
arm64
parisc
s390
unicore32
Thanks,
Rick
On Tue, 2018-11-27 at 16:07 -0800, Rick Edgecombe wrote:
> Since vfree will lazily flush the TLB, but not lazily free the underlying
> pages,
> it often leaves stale TLB entries to freed pages that could get re-used. This
> is
> undesirable for cases where the memory being freed has special permissions
> such
> as executable.
>
> Having callers flush the TLB after calling vfree still leaves a window where
> the pages are freed, but the TLB entry remains. Also the entire operation can
> be
> deferred if the vfree is called from an interrupt and so a TLB flush after
> calling vfree would miss the entire operation. So in order to support this use
> case, a new flag VM_IMMEDIATE_UNMAP is added, that will cause the free
> operation
> to take place like this:
> 1. Unmap
> 2. Flush TLB/Unmap aliases
> 3. Free pages
> In the deferred case these steps are all done by the work queue.
>
> This implementation derives from two sketches from Dave Hansen and
> Andy Lutomirski.
>
> Suggested-by: Dave Hansen <dave.hansen@...el.com>
> Suggested-by: Andy Lutomirski <luto@...nel.org>
> Suggested-by: Will Deacon <will.deacon@....com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
> include/linux/vmalloc.h | 1 +
> mm/vmalloc.c | 13 +++++++++++--
> 2 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 398e9c95cd61..cca6b6b83cf0 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -21,6 +21,7 @@ struct notifier_block; /* in notifier.h */
> #define VM_UNINITIALIZED 0x00000020 /* vm_struct is not fully
> initialized */
> #define VM_NO_GUARD 0x00000040 /* don't add guard page */
> #define VM_KASAN 0x00000080 /* has allocated kasan shadow
> memory */
> +#define VM_IMMEDIATE_UNMAP 0x00000200 /* flush before releasing
> pages */
> /* bits [20..32] reserved for arch specific ioremap internals */
>
> /*
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 97d4b25d0373..68766651b5a7 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1516,6 +1516,14 @@ static void __vunmap(const void *addr, int
> deallocate_pages)
> debug_check_no_obj_freed(area->addr, get_vm_area_size(area));
>
> remove_vm_area(addr);
> +
> + /*
> + * Need to flush the TLB before freeing pages in the case of this flag.
> + * As long as that's happening, unmap aliases.
> + */
> + if (area->flags & VM_IMMEDIATE_UNMAP)
> + vm_unmap_aliases();
> +
> if (deallocate_pages) {
> int i;
>
> @@ -1925,8 +1933,9 @@ EXPORT_SYMBOL(vzalloc_node);
>
> void *vmalloc_exec(unsigned long size)
> {
> - return __vmalloc_node(size, 1, GFP_KERNEL, PAGE_KERNEL_EXEC,
> - NUMA_NO_NODE, __builtin_return_address(0));
> + return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
> + GFP_KERNEL, PAGE_KERNEL_EXEC, VM_IMMEDIATE_UNMAP,
> + NUMA_NO_NODE, __builtin_return_address(0));
> }
>
> #if defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA32)
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