On 2016/1/18 19:56, Mark Rutland wrote: > On Wed, Jan 13, 2016 at 05:10:31PM +0100, Ard Biesheuvel wrote: >> On 13 January 2016 at 15:03, Ard Biesheuvel <[email protected]> >> wrote: >>> On 12 January 2016 at 22:46, Laura Abbott <[email protected]> wrote: >>>> >>>> The range of set_memory_* is currently restricted to the module address >>>> range because of difficulties in breaking down larger block sizes. >>>> vmalloc maps PAGE_SIZE pages so it is safe to use as well. Update the >>>> function ranges and add a comment explaining why the range is restricted >>>> the way it is. >>>> >>>> Signed-off-by: Laura Abbott <[email protected]> >>>> --- >>>> This should let the protections for the eBPF work as expected, I don't >>>> know if there is some sort of self test for thatL. >>> >>> >>> This is going to conflict with my KASLR implementation, since it puts >>> the kernel image right in the middle of the vmalloc area, and the >>> kernel is obviously mapped with block mappings. In fact, I am >>> proposing enabling huge-vmap for arm64 as well, since it seems an >>> improvement generally, but also specifically allows me to unmap the >>> __init section using the generic vunmap code (remove_vm_area). But in >>> general, I think the assumption that the whole vmalloc area is mapped >>> using pages is not tenable. >>> >>> AFAICT, vmalloc still use pages exclusively even with huge-vmap (but >>> ioremap does not). So perhaps it would make sense to check for the >>> VM_ALLOC bit in the VMA flags (which I will not set for the kernel >>> regions either) >>> >> >> Something along these lines, perhaps? >> >> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c >> index 3571c7309c5e..bda0a776c58e 100644 >> --- a/arch/arm64/mm/pageattr.c >> +++ b/arch/arm64/mm/pageattr.c >> @@ -13,6 +13,7 @@ >> #include <linux/kernel.h> >> #include <linux/mm.h> >> #include <linux/module.h> >> +#include <linux/vmalloc.h> >> #include <linux/sched.h> >> >> #include <asm/pgtable.h> >> @@ -44,6 +45,7 @@ static int change_memory_common(unsigned long addr >> unsigned long end = start + size; >> int ret; >> struct page_change_data data; >> + struct vm_struct *area; >> >> if (!PAGE_ALIGNED(addr)) { >> start &= PAGE_MASK; >> @@ -51,10 +53,14 @@ static int change_memory_common(unsigned long addr, >> WARN_ON_ONCE(1); >> } >> >> - if (start < MODULES_VADDR || start >= MODULES_END) >> - return -EINVAL; >> - >> - if (end < MODULES_VADDR || end >= MODULES_END) >> + /* >> + * Check whether the [addr, addr + size) interval is entirely >> + * covered by precisely one VM area that has the VM_ALLOC flag set >> + */ >> + area = find_vm_area((void *)addr); >> + if (!area || >> + end > (unsigned long)area->addr + area->size || >> + !(area->flags & VM_ALLOC)) >> return -EINVAL; >> >> data.set_mask = set_mask; > > Neat. That fixes the fencepost bug too. > > Looks good to me, though as Laura suggested we should have a comment as > to why we limit changes to such regions. Fancy taking her wording below > and spinning this as a patch? > >>>> + /* >>>> + * This check explicitly excludes most kernel memory. Most kernel >>>> + * memory is mapped with a larger page size and breaking down the >>>> + * larger page size without causing TLB conflicts is very >>>> difficult. >>>> + * >>>> + * If you need to call set_memory_* on a range, the recommendation >>>> is >>>> + * to use vmalloc since that range is mapped with pages. >>>> + */ > > Thanks, > Mark. >
Hi Mark, After change the flag, it calls only flush_tlb_kernel_range(), so why not use cpu_replace_ttbr1(swapper_pg_dir)? One more question, does TLB conflict only affect kernel page talbe? There is no problem when spliting the transparent hugepage, right? Thanks, Xishi Qiu > . >
