| Message ID | 20171204141313.31604-6-steve.capper@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 4 December 2017 at 14:13, Steve Capper <steve.capper@arm.com> wrote: > update_mapping_prot assumes that it will be used on the VA for the > kernel .text section. (Via the check virt >= VMALLOC_START) > > Recent kdump patches employ this function to modify the protection of > the direct linear mapping (which is strictly speaking outside of this > area), via mark_linear_text_alias_ro(.). > Isn't that a bug? Is it guaranteed that those protection attributes can be modified without splitting live page tables, and the resulting risk of TLB conflicts? > We "get away" with this as the direct linear mapping currently follows > the VA for the kernel text, so the check passes. > > This patch removes the check in update_mapping_prot allowing us to move > the kernel VA layout without spuriously firing the warning. > > Signed-off-by: Steve Capper <steve.capper@arm.com> > --- > arch/arm64/mm/mmu.c | 6 ------ > 1 file changed, 6 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 58b1ed6fd7ec..c8f486384fe3 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -383,12 +383,6 @@ void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys, > static void update_mapping_prot(phys_addr_t phys, unsigned long virt, > phys_addr_t size, pgprot_t prot) > { > - if (virt < VMALLOC_START) { > - pr_warn("BUG: not updating mapping for %pa at 0x%016lx - outside kernel range\n", > - &phys, virt); > - return; > - } > - > __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, > NO_CONT_MAPPINGS); > > -- > 2.11.0 >
Hi Ard, On Mon, Dec 04, 2017 at 04:01:09PM +0000, Ard Biesheuvel wrote: > On 4 December 2017 at 14:13, Steve Capper <steve.capper@arm.com> wrote: > > update_mapping_prot assumes that it will be used on the VA for the > > kernel .text section. (Via the check virt >= VMALLOC_START) > > > > Recent kdump patches employ this function to modify the protection of > > the direct linear mapping (which is strictly speaking outside of this > > area), via mark_linear_text_alias_ro(.). > > > > Isn't that a bug? Is it guaranteed that those protection attributes > can be modified without splitting live page tables, and the resulting > risk of TLB conflicts? IIUC there is a bug in my earlier patch to flip the kernel VA space round, it should allow addresses from the linear mapping to be processed by update_mapping_prot. I'll update the logic in VA flip patch, so this patch can be removed from the series. It is not apparent to me how mark_linear_text_alias_ro(.) guarantees that no page table entries for the linear map are split, though. Cheers,
On Tue, Dec 12, 2017 at 03:39:23PM +0000, Steve Capper wrote: > It is not apparent to me how mark_linear_text_alias_ro(.) guarantees > that no page table entries for the linear map are split, though. map_mem() ensures that when mapped via __map_memblock(), no contiguous entries are created. Also both ends of the _text..__init_begin would be mapped to the granularity permitted by their alignment so that no later splitting is necessary.
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 58b1ed6fd7ec..c8f486384fe3 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -383,12 +383,6 @@ void __init create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys, static void update_mapping_prot(phys_addr_t phys, unsigned long virt, phys_addr_t size, pgprot_t prot) { - if (virt < VMALLOC_START) { - pr_warn("BUG: not updating mapping for %pa at 0x%016lx - outside kernel range\n", - &phys, virt); - return; - } - __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, NO_CONT_MAPPINGS);
update_mapping_prot assumes that it will be used on the VA for the kernel .text section. (Via the check virt >= VMALLOC_START) Recent kdump patches employ this function to modify the protection of the direct linear mapping (which is strictly speaking outside of this area), via mark_linear_text_alias_ro(.). We "get away" with this as the direct linear mapping currently follows the VA for the kernel text, so the check passes. This patch removes the check in update_mapping_prot allowing us to move the kernel VA layout without spuriously firing the warning. Signed-off-by: Steve Capper <steve.capper@arm.com> --- arch/arm64/mm/mmu.c | 6 ------ 1 file changed, 6 deletions(-)