linux-kernel - Re: [PATCH v14] x86, mce: Add memcpy

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Date:	Thu, 10 Mar 2016 21:26:51 +0200
From:	Mika Penttilä <mika.penttila@...tfour.com>
To:	Tony Luck <tony.luck@...el.com>, Ingo Molnar <mingo@...nel.org>
CC:	<linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v14] x86, mce: Add memcpy_mcsafe()



On 18.02.2016 21:47, Tony Luck wrote:
> Make use of the EXTABLE_FAULT exception table entries to write
> a kernel copy routine that doesn't crash the system if it
> encounters a machine check. Prime use case for this is to copy
> from large arrays of non-volatile memory used as storage.
>
> We have to use an unrolled copy loop for now because current
> hardware implementations treat a machine check in "rep mov"
> as fatal. When that is fixed we can simplify.
>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>
> Is this what we want now?  Return type is a "bool". True means
> that we copied OK, false means that it didn't (this is all that
> Dan says that he needs).  Dropped all the complex code to figure
> out how many bytes we didn't copy as Linus says this isn't the
> right place to do this (and besides we should just make "rep mov"
>
> +
> +	/* Copy successful. Return true */
> +.L_done_memcpy_trap:
> +	xorq %rax, %rax
> +	ret
> +ENDPROC(memcpy_mcsafe)
> +
> +	.section .fixup, "ax"
> +	/* Return false for any failure */
> +.L_memcpy_mcsafe_fail:
> +	mov	$1, %rax
> +	ret
> +
>
But you return 0 == false for success and 1 == true for failure.

--Mika