linux-kernel - Re: [tip:x86/mm] x86/mm: Break out user address space handling

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Date:   Mon, 15 Oct 2018 00:43:57 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     tip-bot for Dave Hansen <tipbot@...or.com>
Cc:     linux-tip-commits@...r.kernel.org, dave.hansen@...ux.intel.com,
        tglx@...utronix.de, linux-kernel@...r.kernel.org, hpa@...or.com,
        mingo@...nel.org, jannh@...gle.com,
        sean.j.christopherson@...el.com, peterz@...radead.org,
        luto@...nel.org
Subject: Re: [tip:x86/mm] x86/mm: Break out user address space handling

tip-bot for Dave Hansen <tipbot@...or.com> writes:

> Commit-ID:  aa37c51b9421d66f7931c5fdcb9ce80c450974be
> Gitweb:     https://git.kernel.org/tip/aa37c51b9421d66f7931c5fdcb9ce80c450974be
> Author:     Dave Hansen <dave.hansen@...ux.intel.com>
> AuthorDate: Fri, 28 Sep 2018 09:02:23 -0700
> Committer:  Peter Zijlstra <peterz@...radead.org>
> CommitDate: Tue, 9 Oct 2018 16:51:15 +0200
>
> x86/mm: Break out user address space handling
>
> The last patch broke out kernel address space handing into its own
> helper.  Now, do the same for user address space handling.
>
> Cc: x86@...nel.org
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Link: http://lkml.kernel.org/r/20180928160223.9C4F6440@viggo.jf.intel.com
> ---
>  arch/x86/mm/fault.c | 47 ++++++++++++++++++++++++++++-------------------
>  1 file changed, 28 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index c7e32f453852..0d1f5d39fc63 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -966,6 +966,7 @@ bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
>  		__bad_area(regs, error_code, address, vma, SEGV_ACCERR);
>  }
>  
> +/* Handle faults in the kernel portion of the address space */
                           ^^^^^^
I believe you mean the __user__ portion of the address space.
Given that the call chain is:

do_user_addr_fault
   handle_mm_fault
      do_sigbus      

>  static void
>  do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
>  	  u32 *pkey, unsigned int fault)
> @@ -1254,14 +1255,11 @@ do_kern_addr_fault(struct pt_regs *regs, unsigned long hw_error_code,
>  }
>  NOKPROBE_SYMBOL(do_kern_addr_fault);
>  
> -/*
> - * This routine handles page faults.  It determines the address,
> - * and the problem, and then passes it off to one of the appropriate
> - * routines.
> - */
> -static noinline void
> -__do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
> -		unsigned long address)
> +/* Handle faults in the user portion of the address space */
> +static inline
> +void do_user_addr_fault(struct pt_regs *regs,
> +			unsigned long hw_error_code,
> +			unsigned long address)
>  {
>  	unsigned long sw_error_code;
>  	struct vm_area_struct *vma;
> @@ -1274,17 +1272,6 @@ __do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
>  	tsk = current;
>  	mm = tsk->mm;
>  
> -	prefetchw(&mm->mmap_sem);
> -
> -	if (unlikely(kmmio_fault(regs, address)))
> -		return;
> -
> -	/* Was the fault on kernel-controlled part of the address space? */
> -	if (unlikely(fault_in_kernel_space(address))) {
> -		do_kern_addr_fault(regs, hw_error_code, address);
> -		return;
> -	}
> -
>  	/* kprobes don't want to hook the spurious faults: */
>  	if (unlikely(kprobes_fault(regs)))
>  		return;
> @@ -1488,6 +1475,28 @@ good_area:
>  
>  	check_v8086_mode(regs, address, tsk);
>  }
> +NOKPROBE_SYMBOL(do_user_addr_fault);
> +
> +/*
> + * This routine handles page faults.  It determines the address,
> + * and the problem, and then passes it off to one of the appropriate
> + * routines.
> + */
> +static noinline void
> +__do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
> +		unsigned long address)
> +{
> +	prefetchw(&current->mm->mmap_sem);
> +
> +	if (unlikely(kmmio_fault(regs, address)))
> +		return;
> +
> +	/* Was the fault on kernel-controlled part of the address space? */
> +	if (unlikely(fault_in_kernel_space(address)))
> +		do_kern_addr_fault(regs, hw_error_code, address);
> +	else
> +		do_user_addr_fault(regs, hw_error_code, address);
> +}
>  NOKPROBE_SYMBOL(__do_page_fault);
>  
>  static nokprobe_inline void

Eric