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Wong" To: Luis Chamberlain Cc: Christophe Leroy , Mike Rapoport , Song Liu , Arnd Bergmann , "Pankaj Raghav (Samsung)" , Stephen Rothwell , Christian Brauner , Pankaj Raghav , Linux Kernel Mailing List , Linux Next Mailing List , ritesh.list@gmail.com, linuxppc-dev@lists.ozlabs.org Subject: Re: linux-next: boot warning after merge of the vfs-brauner tree Message-ID: <20240826211049.GC6082@frogsfrogsfrogs> References: <20240826175931.1989f99e@canb.auug.org.au> <20240826154818.hzqnvofdmaxvuwrh@quentin> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Aug 26, 2024 at 01:52:54PM -0700, Luis Chamberlain wrote: > On Mon, Aug 26, 2024 at 07:43:20PM +0200, Christophe Leroy wrote: > > > > > > Le 26/08/2024 à 17:48, Pankaj Raghav (Samsung) a écrit : > > > On Mon, Aug 26, 2024 at 05:59:31PM +1000, Stephen Rothwell wrote: > > > > Hi all, > > > > > > > > After merging the vfs-brauner tree, today's linux-next boot test (powerpc > > > > pseries_le_defconfig) produced this warning: > > > > > > iomap dio calls set_memory_ro() on the page that is used for sub block > > > zeroing. > > > > > > But looking at powerpc code, they don't support set_memory_ro() for > > > memory region that belongs to the kernel(LINEAR_MAP_REGION_ID). > > > > > > /* > > > * On hash, the linear mapping is not in the Linux page table so > > > * apply_to_existing_page_range() will have no effect. If in the future > > > * the set_memory_* functions are used on the linear map this will need > > > * to be updated. > > > */ > > > if (!radix_enabled()) { > > > int region = get_region_id(addr); > > > > > > if (WARN_ON_ONCE(region != VMALLOC_REGION_ID && region != IO_REGION_ID)) > > > return -EINVAL; > > > } > > > > > > We call set_memory_ro() on the zero page as a extra security measure. > > > I don't know much about powerpc, but looking at the comment, is it just > > > adding the following to support it in powerpc: > > > > > > diff --git a/arch/powerpc/mm/pageattr.c b/arch/powerpc/mm/pageattr.c > > > index ac22bf28086fa..e6e0b40ba6db4 100644 > > > --- a/arch/powerpc/mm/pageattr.c > > > +++ b/arch/powerpc/mm/pageattr.c > > > @@ -94,7 +94,9 @@ int change_memory_attr(unsigned long addr, int numpages, long action) > > > if (!radix_enabled()) { > > > int region = get_region_id(addr); > > > - if (WARN_ON_ONCE(region != VMALLOC_REGION_ID && region != IO_REGION_ID)) > > > + if (WARN_ON_ONCE(region != VMALLOC_REGION_ID && > > > + region != IO_REGION_ID && > > > + region != LINEAR_MAP_REGION_ID)) > > > return -EINVAL; > > > } > > > #endif > > > > By doing this you will just hide the fact that it didn't work. > > > > See commit 1f9ad21c3b38 ("powerpc/mm: Implement set_memory() routines") for > > details. The linear memory region is not mapped using page tables so > > set_memory_ro() will have no effect on it. > > > > You can either use vmalloc'ed pages, or do a const static allocation at > > buildtime so that it will be allocated in the kernel static rodata area. > > > > By the way, your code should check the value returned by set_memory_ro(), > > there is some work in progress to make it mandatory, see > > https://github.com/KSPP/linux/issues/7 > > Our users expect contiguous memory [0] and so we use alloc_pages() here, > so if we're architecture limitted by this I'd rather we just remove the > set_memory_ro() only for PPC, I don't see why other have to skip this. Just drop it, then. --D > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c > index c02b266bba52..aba5cde89e14 100644 > --- a/fs/iomap/direct-io.c > +++ b/fs/iomap/direct-io.c > @@ -775,14 +775,22 @@ EXPORT_SYMBOL_GPL(iomap_dio_rw); > > static int __init iomap_dio_init(void) > { > + int ret; > + > zero_page = alloc_pages(GFP_KERNEL | __GFP_ZERO, > IOMAP_ZERO_PAGE_ORDER); > > if (!zero_page) > return -ENOMEM; > > - set_memory_ro((unsigned long)page_address(zero_page), > - 1U << IOMAP_ZERO_PAGE_ORDER); > - return 0; > + if (IS_ENABLED(CONFIG_PPC)) > + return 0; > + > + ret = set_memory_ro((unsigned long)page_address(zero_page), > + 1U << IOMAP_ZERO_PAGE_ORDER); > + if (ret) > + free_pages((unsigned long) zero_page, IOMAP_ZERO_PAGE_ORDER); > + > + return ret; > } > fs_initcall(iomap_dio_init); > > Thoughts? > > [0] https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?h=vfs.blocksize&id=d940b3b7b76b409b0550fdf2de6dc2183f01526f > > Luis