On Thu, Nov 10, 2022 at 08:45:07AM +0530, Anshuman Khandual wrote:
> On 11/10/22 00:48, Catalin Marinas wrote:
> > On Thu, Oct 27, 2022 at 08:09:15AM +0530, Anshuman Khandual wrote:
> >> +#define __HAVE_ARCH_PTEP_MODIFY_PROT_TRANSACTION
> >> +static inline pte_t ptep_modify_prot_start(struct vm_area_struct *vma,
> >> + unsigned long addr,
> >> + pte_t *ptep)
> >> +{
> >> + pte_t pte = ptep_get_and_clear(vma->vm_mm, addr, ptep);
> >>
> >> + if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> >> + /*
> >> + * Break-before-make (BBM) is required for all user space mappings
> >> + * when the permission changes from executable to non-executable
> >> + * in cases where cpu is affected with errata #2645198.
> >> + */
> >> + if (pte_user_exec(pte) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> >> + __flush_tlb_range(vma, addr, addr + PAGE_SIZE, PAGE_SIZE, false, 3);
> >
> > Why not flush_tlb_page() here?
> >
> > But more importantly, can we not use ptep_clear_flush() instead (and
>
> Something like ...
>
> ptep_modify_prot_start -
>
> if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> return ptep_clear_flush(vma, addr, ptep);
> } else {
> return ptep_get_and_clear(vma->vm_mm, addr, ptep);
> }
Yes, this should work but avoid the 'else' when you have a return, so
something like:
if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198) &&
cpus_have_const_cap(ARM64_WORKAROUND_2645198) &&
pte_user_exec(READ_ONCE(*ptep)))
return ptep_clear_flush(vma, addr, ptep);
return ptep_get_and_clear(vma->vm_mm, addr, ptep);
> > huge_ptep_clear_flush())? They return the pte and do the TLBI.
>
> huge_ptep_modify_prot_start -
>
> if (IS_ENABLED(CONFIG_ARM64_WORKAROUND_2645198)) {
> if (pte_user_exec(READ_ONCE(*ptep)) && cpus_have_const_cap(ARM64_WORKAROUND_2645198))
> return huge_ptep_clear_flush(vma, addr, ptep);
> } else {
> return huge_ptep_get_and_clear(vma->vm_mm, addr, ptep);
> }
>
> pte_user_exec(READ_ONCE(*ptep) should identify an user exec mapping even though
> ptep represents a cont PTE/PMD huge page ? OR should huge_ptep_get() helper be
> used instead ?
This should work as a shortcut. The contiguous ptes should all be the
same, so it's sufficient to check one of them.
--
Catalin
