linux-kernel - Re: [RFC PATCH 2/4] x86/fault: Attempt to fixup unhandled #PF in vDSO before signaling

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Date:   Thu, 6 Dec 2018 10:17:34 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...capital.net>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Josh Triplett <josh@...htriplett.org>
Subject: Re: [RFC PATCH 2/4] x86/fault: Attempt to fixup unhandled #PF in vDSO
 before signaling

>  #define CREATE_TRACE_POINTS
>  #include <asm/trace/exceptions.h>
> @@ -928,6 +929,9 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
>  		if (address >= TASK_SIZE_MAX)
>  			error_code |= X86_PF_PROT;
>  
> +		if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
> +			return;
> +
>  		if (likely(show_unhandled_signals))
>  			show_signal_msg(regs, error_code, address, tsk);

I'd preferably like to get this plugged into the page fault code before
we get to the "bad_area" handling.  This plugs it in near the erratum
handling which seems really late to me.

> @@ -1045,6 +1049,9 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address,
>  	if (is_prefetch(regs, error_code, address))
>  		return;
>  
> +	if (fixup_vdso_exception(regs, X86_TRAP_PF, error_code, address))
> +		return;
> +
>  	set_signal_archinfo(address, error_code);
>  
>  #ifdef CONFIG_MEMORY_FAILURE

This *seems* really late to me.  We've already called into the mm fault
handling code to try and handle the fault and they told us it was
VM_FAULT_SIGBUS.  Shouldn't we have just detected that it was in the
vDSO first and not even called the handling code?