Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map
From: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Date: 2020-10-26 00:39:20
Also in:
linux-arm-kernel, linux-mm, linux-pm, linux-riscv, linux-s390, lkml, sparclinux
On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote:
From: Mike Rapoport <redacted> When DEBUG_PAGEALLOC or ARCH_HAS_SET_DIRECT_MAP is enabled a page may be not present in the direct map and has to be explicitly mapped before it could be copied. On arm64 it is possible that a page would be removed from the direct map using set_direct_map_invalid_noflush() but __kernel_map_pages() will refuse to map this page back if DEBUG_PAGEALLOC is disabled.
It looks to me that arm64 __kernel_map_pages() will still attempt to map it if rodata_full is true, how does this happen?
quoted hunk ↗ jump to hunk
Explicitly use set_direct_map_{default,invalid}_noflush() for ARCH_HAS_SET_DIRECT_MAP case and debug_pagealloc_map_pages() for DEBUG_PAGEALLOC case. While on that, rename kernel_map_pages() to hibernate_map_page() and drop numpages parameter. Signed-off-by: Mike Rapoport <redacted> --- kernel/power/snapshot.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-)diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c index fa499466f645..ecb7b32ce77c 100644 --- a/kernel/power/snapshot.c +++ b/kernel/power/snapshot.c@@ -76,16 +76,25 @@ static inline voidhibernate_restore_protect_page(void *page_address) {} static inline void hibernate_restore_unprotect_page(void *page_address) {} #endif /* CONFIG_STRICT_KERNEL_RWX && CONFIG_ARCH_HAS_SET_MEMORY */ -#if defined(CONFIG_DEBUG_PAGEALLOC) || defined(CONFIG_ARCH_HAS_SET_DIRECT_MAP) -static inline void -kernel_map_pages(struct page *page, int numpages, int enable) +static inline void hibernate_map_page(struct page *page, int enable) { - __kernel_map_pages(page, numpages, enable); + if (IS_ENABLED(CONFIG_ARCH_HAS_SET_DIRECT_MAP)) { + unsigned long addr = (unsigned long)page_address(page); + int ret; + + if (enable) + ret = set_direct_map_default_noflush(page); + else + ret = set_direct_map_invalid_noflush(page); + + if (WARN_ON(ret)) + return; + + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); + } else { + debug_pagealloc_map_pages(page, 1, enable); + } } -#else -static inline void -kernel_map_pages(struct page *page, int numpages, int enable) {} -#endif static int swsusp_page_is_free(struct page *); static void swsusp_set_page_forbidden(struct page *);@@ -1366,9 +1375,9 @@ static void safe_copy_page(void *dst, structpage *s_page) if (kernel_page_present(s_page)) { do_copy_page(dst, page_address(s_page)); } else { - kernel_map_pages(s_page, 1, 1); + hibernate_map_page(s_page, 1); do_copy_page(dst, page_address(s_page)); - kernel_map_pages(s_page, 1, 0); + hibernate_map_page(s_page, 0); } }
If somehow a page was unmapped such that set_direct_map_default_noflush() would fail, then this code introduces a WARN, but it will still try to read the unmapped page. Why not just have the WARN's inside of __kernel_map_pages() if they fail and then have a warning for the debug page alloc cases as well? Since logic around both expects them not to fail.