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Date:   Fri, 24 Sep 2021 10:29:28 +1200
From:   Barry Song <21cnbao@...il.com>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        David Hildenbrand <david@...hat.com>,
        Chen Huang <chenhuang5@...wei.com>,
        "Bodeddula, Balasubramaniam" <bodeddub@...zon.com>,
        Jonathan Corbet <corbet@....net>,
        Matthew Wilcox <willy@...radead.org>,
        Xiongchun duan <duanxiongchun@...edance.com>,
        fam.zheng@...edance.com, Muchun Song <smuchun@...il.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v3 4/4] selftests: vm: add a hugetlb test case

On Wed, Sep 22, 2021 at 10:27 PM Muchun Song <songmuchun@...edance.com> wrote:
>
> Since the head vmemmap page frame associated with each HugeTLB page is
> reused, we should hide the PG_head flag of tail struct page from the
> user. Add a tese case to check whether it is work properly. The test
> steps are as follows.
>
>   1) alloc 2MB hugeTLB
>   2) get each page frame
>   3) apply those APIs in each page frame
>   4) Those APIs work completely the same as before.
>
> Reading the flags of a page by /proc/kpageflags is done in
> stable_page_flags(), which has invoked PageHead(), PageTail(),
> PageCompound() and compound_head(). If those APIs work properly, the
> head page must have 15 and 17 bits set. And tail pages must have 16
> and 17 bits set but 15 bit unset. Those flags are checked in
> check_page_flags().
>
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> ---
>  tools/testing/selftests/vm/vmemmap_hugetlb.c | 144 +++++++++++++++++++++++++++
>  1 file changed, 144 insertions(+)
>  create mode 100644 tools/testing/selftests/vm/vmemmap_hugetlb.c
>
> diff --git a/tools/testing/selftests/vm/vmemmap_hugetlb.c b/tools/testing/selftests/vm/vmemmap_hugetlb.c
> new file mode 100644
> index 000000000000..4cc74dd4c333
> --- /dev/null
> +++ b/tools/testing/selftests/vm/vmemmap_hugetlb.c
> @@ -0,0 +1,144 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * A test case of using hugepage memory in a user application using the
> + * mmap system call with MAP_HUGETLB flag.  Before running this program
> + * make sure the administrator has allocated enough default sized huge
> + * pages to cover the 2 MB allocation.
> + *
> + * For ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
> + * That means the addresses starting with 0x800000... will need to be
> + * specified.  Specifying a fixed address is not required on ppc64, i386
> + * or x86_64.
> + */
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <unistd.h>
> +#include <sys/mman.h>
> +#include <fcntl.h>
> +
> +#define MAP_LENGTH             (2UL * 1024 * 1024)
> +
> +#ifndef MAP_HUGETLB
> +#define MAP_HUGETLB            0x40000 /* arch specific */
> +#endif
> +
> +#define PAGE_SIZE              4096
> +
> +#define PAGE_COMPOUND_HEAD     (1UL << 15)
> +#define PAGE_COMPOUND_TAIL     (1UL << 16)
> +#define PAGE_HUGE              (1UL << 17)
> +
> +#define HEAD_PAGE_FLAGS                (PAGE_COMPOUND_HEAD | PAGE_HUGE)
> +#define TAIL_PAGE_FLAGS                (PAGE_COMPOUND_TAIL | PAGE_HUGE)
> +
> +#define PM_PFRAME_BITS         55
> +#define PM_PFRAME_MASK         ~((1UL << PM_PFRAME_BITS) - 1)
> +

better to move the comment here:

+ * For ia64 architecture, Linux kernel reserves Region number 4 for hugepages.
+ * That means the addresses starting with 0x800000... will need to be
+ * specified.  Specifying a fixed address is not required on ppc64, i386
+ * or x86_64.

With the change,

Reviewed-by: Barry Song <song.bao.hua@...ilicon.com>

> +/* Only ia64 requires this */
> +#ifdef __ia64__
> +#define MAP_ADDR               (void *)(0x8000000000000000UL)
> +#define MAP_FLAGS              (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB | MAP_FIXED)
> +#else
> +#define MAP_ADDR               NULL
> +#define MAP_FLAGS              (MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB)
> +#endif
> +
> +static void write_bytes(char *addr, size_t length)
> +{
> +       unsigned long i;
> +
> +       for (i = 0; i < length; i++)
> +               *(addr + i) = (char)i;
> +}
> +
> +static unsigned long virt_to_pfn(void *addr)
> +{
> +       int fd;
> +       unsigned long pagemap;
> +
> +       fd = open("/proc/self/pagemap", O_RDONLY);
> +       if (fd < 0)
> +               return -1UL;
> +
> +       lseek(fd, (unsigned long)addr / PAGE_SIZE * sizeof(pagemap), SEEK_SET);
> +       read(fd, &pagemap, sizeof(pagemap));
> +       close(fd);
> +
> +       return pagemap & ~PM_PFRAME_MASK;
> +}
> +
> +static int check_page_flags(unsigned long pfn)
> +{
> +       int fd, i;
> +       unsigned long pageflags;
> +
> +       fd = open("/proc/kpageflags", O_RDONLY);
> +       if (fd < 0)
> +               return -1;
> +
> +       lseek(fd, pfn * sizeof(pageflags), SEEK_SET);
> +
> +       read(fd, &pageflags, sizeof(pageflags));
> +       if ((pageflags & HEAD_PAGE_FLAGS) != HEAD_PAGE_FLAGS) {
> +               close(fd);
> +               printf("Head page flags (%lx) is invalid\n", pageflags);
> +               return -1;
> +       }
> +
> +       /*
> +        * pages other than the first page must be tail and shouldn't be head;
> +        * this also verifies kernel has correctly set the fake page_head to tail
> +        * while hugetlb_free_vmemmap is enabled.
> +        */
> +       for (i = 1; i < MAP_LENGTH / PAGE_SIZE; i++) {
> +               read(fd, &pageflags, sizeof(pageflags));
> +               if ((pageflags & TAIL_PAGE_FLAGS) != TAIL_PAGE_FLAGS ||
> +                   (pageflags & HEAD_PAGE_FLAGS) == HEAD_PAGE_FLAGS) {
> +                       close(fd);
> +                       printf("Tail page flags (%lx) is invalid\n", pageflags);
> +                       return -1;
> +               }
> +       }
> +
> +       close(fd);
> +
> +       return 0;
> +}
> +
> +int main(int argc, char **argv)
> +{
> +       void *addr;
> +       unsigned long pfn;
> +
> +       addr = mmap(MAP_ADDR, MAP_LENGTH, PROT_READ | PROT_WRITE, MAP_FLAGS, -1, 0);
> +       if (addr == MAP_FAILED) {
> +               perror("mmap");
> +               exit(1);
> +       }
> +
> +       /* Trigger allocation of HugeTLB page. */
> +       write_bytes(addr, MAP_LENGTH);
> +
> +       pfn = virt_to_pfn(addr);
> +       if (pfn == -1UL) {
> +               munmap(addr, MAP_LENGTH);
> +               perror("virt_to_pfn");
> +               exit(1);
> +       }
> +
> +       printf("Returned address is %p whose pfn is %lx\n", addr, pfn);
> +
> +       if (check_page_flags(pfn) < 0) {
> +               munmap(addr, MAP_LENGTH);
> +               perror("check_page_flags");
> +               exit(1);
> +       }
> +
> +       /* munmap() length of MAP_HUGETLB memory must be hugepage aligned */
> +       if (munmap(addr, MAP_LENGTH)) {
> +               perror("munmap");
> +               exit(1);
> +       }
> +
> +       return 0;
> +}
> --
> 2.11.0
>

Thanks
barry

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