Re: [PATCH 2/9] hugetlb/userfaultfd: Forbid huge pmd sharing when uffd enabled

[Peter Xu]

On Fri, Jan 15, 2021 at 11:04:44AM -0800, Axel Rasmussen wrote:

[...]

> @@ -947,4 +948,15 @@ static inline __init void hugetlb_cma_check(void)
>  }
>  #endif
>  
> +static inline bool want_pmd_share(struct vm_area_struct *vma)
> +{
> +#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
> +	if (uffd_disable_huge_pmd_share(vma))
> +		return false;
> +	return true;
> +#else
> +	return false;
> +#endif
> +}

I got syzbot complains about this chunk when compile some other archs outside
x86, probably because CONFIG_ARCH_WANT_HUGE_PMD_SHARE can be defined without
CONFIG_USERFAULTFD.  I don't know why it didn't complain here, so just a fyi
that I've pushed some new version to the online repo so that they should have
been fixed.  For example, for this patch:

https://github.com/xzpeter/linux/commit/0fd01db2c9ac3ab8600f3f7df23cf28fddcfee1b

static inline bool want_pmd_share(struct vm_area_struct *vma)
{
#ifdef CONFIG_USERFAULTFD
	if (uffd_disable_huge_pmd_share(vma))
		return false;
#endif

#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
	return true;
#else
	return false;
#endif
}

Thanks,

-- 
Peter Xu