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Message-ID: <Z-cnmklGUojMzsUF@kernel.org>
Date: Sat, 29 Mar 2025 01:50:02 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Dev Jain <dev.jain@....com>
Cc: catalin.marinas@....com, will@...nel.org, gshan@...hat.com,
steven.price@....com, suzuki.poulose@....com,
tianyaxiong@...inos.cn, ardb@...nel.org, david@...hat.com,
ryan.roberts@....com, urezki@...il.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: pageattr: Explicitly bail out when changing
permissions for vmalloc_huge mappings
On Fri, Mar 28, 2025 at 11:51:03AM +0530, Dev Jain wrote:
> arm64 uses apply_to_page_range to change permissions for kernel VA mappings,
for vmalloc mappings ^
arm64 does not allow changing permissions to any VA address right now.
> which does not support changing permissions for leaf mappings. This function
> will change permissions until it encounters a leaf mapping, and will bail
> out. To avoid this partial change, explicitly disallow changing permissions
> for VM_ALLOW_HUGE_VMAP mappings.
>
> Signed-off-by: Dev Jain <dev.jain@....com>
> ---
> arch/arm64/mm/pageattr.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index 39fd1f7ff02a..8337c88eec69 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -96,7 +96,7 @@ static int change_memory_common(unsigned long addr, int numpages,
> * we are operating on does not result in such splitting.
> *
> * Let's restrict ourselves to mappings created by vmalloc (or vmap).
> - * Those are guaranteed to consist entirely of page mappings, and
> + * Disallow VM_ALLOW_HUGE_VMAP vmalloc mappings so that
I'd keep mention of page mappings in the comment, e.g
* Disallow VM_ALLOW_HUGE_VMAP mappings to guarantee that only page
* mappings are updated and splitting is never needed.
With this and changelog updates Ryan asked for
Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
> * splitting is never needed.
> *
> * So check whether the [addr, addr + size) interval is entirely
> @@ -105,7 +105,7 @@ static int change_memory_common(unsigned long addr, int numpages,
> area = find_vm_area((void *)addr);
> if (!area ||
> end > (unsigned long)kasan_reset_tag(area->addr) + area->size ||
> - !(area->flags & VM_ALLOC))
> + ((area->flags & (VM_ALLOC | VM_ALLOW_HUGE_VMAP)) != VM_ALLOC))
> return -EINVAL;
>
> if (!numpages)
> --
> 2.30.2
>
--
Sincerely yours,
Mike.
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