Luis Chamberlain <mcgrof@xxxxxxxxxx> writes: > On Mon, Aug 26, 2024 at 02:10:49PM -0700, Darrick J. Wong wrote: >> 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. Looks like not a standard thing to do for kernel linear memory map region then and maybe few other archs could be ignoring too? >> >> Just drop it, then. > > OK sent a patch for that. > Thanks for fixing it! -ritesh