Hi Oscar,

On Wed, 10 Mar 2021 at 03:11, Oscar Salvador osalvador@suse.de wrote:

When sizeof(struct page) is not a power of 2, sections do not span a PMD anymore and so when populating them some parts of the PMD will remain unused. Because of this, PMDs will be left behind when depopulating sections since remove_pmd_table() thinks that those unused parts are still in use.

Fix this by marking the unused parts with PAGE_UNUSED, so memchr_inv() will do the right thing and will let us free the PMD when the last user of it is gone.

This patch is based on a similar patch by David Hildenbrand:

https://lore.kernel.org/linux-mm/20200722094558.9828-9-david@redhat.com/

Signed-off-by: Oscar Salvador osalvador@suse.de Reviewed-by: David Hildenbrand david@redhat.com Acked-by: Dave Hansen dave.hansen@linux.intel.com

---

arch/x86/mm/init_64.c | 65 +++++++++++++++++++++++++++++++++++++++++---------- 1 file changed, 53 insertions(+), 12 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c index 9ecb3c488ac8..d93b36856ed3 100644 --- a/arch/x86/mm/init_64.c +++ b/arch/x86/mm/init_64.c @@ -826,6 +826,51 @@ void __init paging_init(void) zone_sizes_init(); }

+#ifdef CONFIG_SPARSEMEM_VMEMMAP +#define PAGE_UNUSED 0xFD

+/* Returns true if the PMD is completely unused and thus it can be freed */ +static bool __meminit vmemmap_pmd_is_unused(unsigned long addr, unsigned long end) +{

•   unsigned long start = ALIGN_DOWN(addr, PMD_SIZE);
  

•   memset((void *)addr, PAGE_UNUSED, end - addr);
  

•   return !memchr_inv((void *)start, PAGE_UNUSED, PMD_SIZE);
  

+}

+static void __meminit vmemmap_use_sub_pmd(unsigned long start) +{

•   /*
  

•    * As we expect to add in the same granularity as we remove, it's
  

•    * sufficient to mark only some piece used to block the memmap page from
  

•    * getting removed when removing some other adjacent memmap (just in
  

•    * case the first memmap never gets initialized e.g., because the memory
  

•    * block never gets onlined).
  

•    */
  

•   memset((void *)start, 0, sizeof(struct page));
  

+}

+static void __meminit vmemmap_use_new_sub_pmd(unsigned long start, unsigned long end) +{

•   /*
  

•    * Could be our memmap page is filled with PAGE_UNUSED already from a
  

•    * previous remove. Make sure to reset it.
  

•    */
  

•   vmemmap_use_sub_pmd(start);
  

•   /*
  

•    * Mark with PAGE_UNUSED the unused parts of the new memmap range
  

•    */
  

•   if (!IS_ALIGNED(start, PMD_SIZE))
  

•           memset((void *)start, PAGE_UNUSED,
  

•                   start - ALIGN_DOWN(start, PMD_SIZE));
  

•   if (!IS_ALIGNED(end, PMD_SIZE))
  

•           memset((void *)end, PAGE_UNUSED,
  

•                   ALIGN(end, PMD_SIZE) - end);
  

+} +#endif

/*

• Memory hotplug specific functions

*/ @@ -871,8 +916,6 @@ int arch_add_memory(int nid, u64 start, u64 size, return add_pages(nid, start_pfn, nr_pages, params); }

-#define PAGE_INUSE 0xFD

static void __meminit free_pagetable(struct page *page, int order) { unsigned long magic; @@ -1006,7 +1049,6 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, unsigned long next, pages = 0; pte_t *pte_base; pmd_t *pmd;

•   void *page_addr;
  
    pmd = pmd_start + pmd_index(addr);
    for (; addr < end; addr = next, pmd++) {
  

@@ -1026,20 +1068,13 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end, pmd_clear(pmd); spin_unlock(&init_mm.page_table_lock); pages++;

•                   } else {
  

•                           /* If here, we are freeing vmemmap pages. */
  

•                           memset((void *)addr, PAGE_INUSE, next - addr);
  

•                           page_addr = page_address(pmd_page(*pmd));
  

•                           if (!memchr_inv(page_addr, PAGE_INUSE,
  

•                                           PMD_SIZE)) {
  

•                   } else if (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP) &&
  

•                              vmemmap_pmd_is_unused(addr, next)) {
                                    free_hugepage_table(pmd_page(*pmd),
                                                        altmap);
  

•                                   spin_lock(&init_mm.page_table_lock);
                                    pmd_clear(pmd);
                                    spin_unlock(&init_mm.page_table_lock);
  

•                           }
                    }
  
                    continue;
  

@@ -1492,11 +1527,17 @@ static int __meminit vmemmap_populate_hugepages(unsigned long start,

                            addr_end = addr + PMD_SIZE;
                            p_end = p + PMD_SIZE;

•                           if (!IS_ALIGNED(addr, PMD_SIZE) ||
  

•                               !IS_ALIGNED(next, PMD_SIZE))
  

•                                   vmemmap_use_new_sub_pmd(addr, next);
  

•                           continue;
                    } else if (altmap)
                            return -ENOMEM; /* no fallback */
            } else if (pmd_large(*pmd)) {
                    vmemmap_verify((pte_t *)pmd, node, addr, next);
  

•                   vmemmap_use_sub_pmd(addr);
  

While building the linux next 20210310 tag for x86_64 architecture with clang-12 and gcc-9 the following warnings / errors were noticed.

arch/x86/mm/init_64.c:1585:6: error: implicit declaration of function 'vmemmap_use_new_sub_pmd' [-Werror,-Wimplicit-function-declaration] vmemmap_use_new_sub_pmd(addr, next); ^ arch/x86/mm/init_64.c:1591:4: error: implicit declaration of function 'vmemmap_use_sub_pmd' [-Werror,-Wimplicit-function-declaration] vmemmap_use_sub_pmd(addr, next); ^ 2 errors generated. make[3]: *** [scripts/Makefile.build:271: arch/x86/mm/init_64.o] Error 1

Reported-by: Naresh Kamboju naresh.kamboju@linaro.org

Steps to reproduce: ------------------- # TuxMake is a command line tool and Python library that provides # portable and repeatable Linux kernel builds across a variety of # architectures, toolchains, kernel configurations, and make targets. # # TuxMake supports the concept of runtimes. # See https://docs.tuxmake.org/runtimes/, for that to work it requires # that you install podman or docker on your system. # # To install tuxmake on your system globally: # sudo pip3 install -U tuxmake # # See https://docs.tuxmake.org/ for complete documentation.

tuxmake --runtime podman --target-arch x86_64 --toolchain clang-12 --kconfig defconfig --kconfig-add https://builds.tuxbuild.com/1pYCPt4WlgSfSdv1BULm6ABINeJ/config

Build pipeline error link, https://gitlab.com/Linaro/lkft/mirrors/next/linux-next/-/jobs/1085496613#L42...