linux-kernel - Re: [PATCH v3 1/4] selftests/mm: virtual_address_range: mmap() without PROT

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Message-ID: <8b402b5d-ca7a-4dc1-867d-013823c8ab00@arm.com>
Date: Mon, 13 Jan 2025 21:16:12 +0530
From: Dev Jain <dev.jain@....com>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
 Andrew Morton <akpm@...ux-foundation.org>, Shuah Khan <shuah@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, David Hildenbrand <david@...hat.com>
Cc: linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] selftests/mm: virtual_address_range: mmap()
 without PROT_WRITE



On 13/01/25 6:45 pm, Thomas Weißschuh wrote:
> When mapping a larger chunk than physical memory is available with
> PROT_WRITE and overcommit is disabled, the mapping will fail.
> This will prevent the test from running on systems with less then ~1GiB
> of memory and triggering an inscrutinable test failure.
> As the mappings are never written to anyways, the flag can be removed.
> 
> Fixes: 010409649885 ("selftests/mm: confirm VA exhaustion without reliance on correctness of mmap()")
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> Acked-by: David Hildenbrand <david@...hat.com>
> Acked-by: Dev Jain <dev.jain@....com>
> ---
>   tools/testing/selftests/mm/virtual_address_range.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/virtual_address_range.c b/tools/testing/selftests/mm/virtual_address_range.c
> index 2a2b69e91950a37999f606847c9c8328d79890c2..ea6ccf49ef4c552f26317c2a40b09bca1a677f8f 100644
> --- a/tools/testing/selftests/mm/virtual_address_range.c
> +++ b/tools/testing/selftests/mm/virtual_address_range.c
> @@ -166,7 +166,7 @@ int main(int argc, char *argv[])
>   	ksft_set_plan(1);
>   
>   	for (i = 0; i < NR_CHUNKS_LOW; i++) {
> -		ptr[i] = mmap(NULL, MAP_CHUNK_SIZE, PROT_READ | PROT_WRITE,
> +		ptr[i] = mmap(NULL, MAP_CHUNK_SIZE, PROT_READ,
>   			      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>   
>   		if (ptr[i] == MAP_FAILED) {
> @@ -186,7 +186,7 @@ int main(int argc, char *argv[])
>   
>   	for (i = 0; i < NR_CHUNKS_HIGH; i++) {
>   		hint = hint_addr();
> -		hptr[i] = mmap(hint, MAP_CHUNK_SIZE, PROT_READ | PROT_WRITE,
> +		hptr[i] = mmap(hint, MAP_CHUNK_SIZE, PROT_READ,
>   			       MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>   
>   		if (hptr[i] == MAP_FAILED)
> 

Just noticed a thing: I believe the fix commit you are looking for is
4e5ce33ceb32. My commit which you mention is not responsible for 
introducing the problem you are solving.