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Mon, 26 Oct 2020 20:16:14 +1100 (AEDT) Received: from kernel.org (unknown [87.70.96.83]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B98A52076D; Mon, 26 Oct 2020 09:15:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603703772; bh=pop+GQ7xmiCTdiMy7B7WjKex9h5Ro/VhE9OJ7tV4F50=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QcsGfbDXA790Gjo2jSURCFd11bM6efKFvKFsUWyXN44//16ZrE/paF3TuAJVQB4Rr mz78GEiiRdCUDL2DmSZQKmV3QOTV3troBBj6WAvp8CVBS8VJ7TSHYavrFKSKMBbgmb ZMwdKEfod10n2z6aUqC33jSQaZUMycRaW8U5Xg+0= Date: Mon, 26 Oct 2020 11:15:54 +0200 From: Mike Rapoport To: "Edgecombe, Rick P" Subject: Re: [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Message-ID: <20201026091554.GB1154158@kernel.org> References: <20201025101555.3057-1-rppt@kernel.org> <20201025101555.3057-3-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "david@redhat.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "paulus@samba.org" , "pavel@ucw.cz" , "hpa@zytor.com" , "sparclinux@vger.kernel.org" , "cl@linux.com" , "will@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-s390@vger.kernel.org" , "x86@kernel.org" , "rppt@linux.ibm.com" , "borntraeger@de.ibm.com" , "mingo@redhat.com" , "rientjes@google.com" , "Brown, Len" , "aou@eecs.berkeley.edu" , "gor@linux.ibm.com" , "linux-pm@vger.kernel.org" , "hca@linux.ibm.com" , "bp@alien8.de" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "tglx@linutronix.de" , "akpm@linux-foundation.org" , "linux-arm-kernel@lists.infradead.org" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "penberg@kernel.org" , "palmer@dabbelt.com" , "iamjoonsoo.kim@lge.com" , "linuxppc-dev@lists.ozlabs.org" , "davem@davemloft.net" Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Oct 26, 2020 at 12:38:32AM +0000, Edgecombe, Rick P wrote: > On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote: > > From: Mike Rapoport > > > > 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? Unless I misread the code, arm64 requires both rodata_full and debug_pagealloc_enabled() to be true for __kernel_map_pages() to do anything. But rodata_full condition applies to set_direct_map_*_noflush() as well, so with !rodata_full the linear map won't be ever changed. > > 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 > > --- > > 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 void > > hibernate_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, struct > > page *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. The intention of this series is to disallow usage of __kernel_map_pages() when DEBUG_PAGEALLOC=n. I'll update this patch to better handle possible errors, but I still want to keep WARN in the caller. -- Sincerely yours, Mike.