linux-kernel - Re: [PATCH v3 7/7] selftest/mm: ksm_functional_tests: Add PROT

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Date:   Thu, 3 Aug 2023 15:06:40 -0400
From:   Peter Xu <peterx@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        liubo <liubo254@...wei.com>,
        Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        John Hubbard <jhubbard@...dia.com>,
        Mel Gorman <mgorman@...e.de>, Shuah Khan <shuah@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v3 7/7] selftest/mm: ksm_functional_tests: Add PROT_NONE
 test

On Thu, Aug 03, 2023 at 04:32:08PM +0200, David Hildenbrand wrote:
> Let's test whether merging and unmerging in PROT_NONE areas works as
> expected.
> 
> Pass a page protection to mmap_and_merge_range(), which will trigger
> an mprotect() after writing to the pages, but before enabling merging.
> 
> Make sure that unsharing works as expected, by performing a ptrace write
> (using /proc/self/mem) and by setting MADV_UNMERGEABLE.
> 
> Note that this implicitly tests that ptrace writes in an inaccessible
> (PROT_NONE) mapping work as expected.
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

[...]

> +static void test_prot_none(void)
> +{
> +	const unsigned int size = 2 * MiB;
> +	char *map;
> +	int i;
> +
> +	ksft_print_msg("[RUN] %s\n", __func__);
> +
> +	map = mmap_and_merge_range(0x11, size, PROT_NONE, false);
> +	if (map == MAP_FAILED)
> +		goto unmap;
> +
> +	/* Store a unique value in each page on one half using ptrace */
> +	for (i = 0; i < size / 2; i += pagesize) {
> +		lseek(mem_fd, (uintptr_t) map + i, SEEK_SET);
> +		if (write(mem_fd, &i, sizeof(size)) != sizeof(size)) {

sizeof(i)?  May not matter a huge lot, though..

> +			ksft_test_result_fail("ptrace write failed\n");
> +			goto unmap;
> +		}
> +	}

Acked-by: Peter Xu <peterx@...hat.com>

-- 
Peter Xu