Re: [PATCH v13 4/5] arm64: support copy_mc_[user]_highpage()

[Tong Tiangen <tongtiangen@huawei.com>]

在 2025/2/13 1:11, Catalin Marinas 写道:
> On Mon, Dec 09, 2024 at 10:42:56AM +0800, Tong Tiangen wrote:
>> Currently, many scenarios that can tolerate memory errors when copying page
>> have been supported in the kernel[1~5], all of which are implemented by
>> copy_mc_[user]_highpage(). arm64 should also support this mechanism.
>>
>> Due to mte, arm64 needs to have its own copy_mc_[user]_highpage()
>> architecture implementation, macros __HAVE_ARCH_COPY_MC_HIGHPAGE and
>> __HAVE_ARCH_COPY_MC_USER_HIGHPAGE have been added to control it.
>>
>> Add new helper copy_mc_page() which provide a page copy implementation with
>> hardware memory error safe. The code logic of copy_mc_page() is the same as
>> copy_page(), the main difference is that the ldp insn of copy_mc_page()
>> contains the fixup type EX_TYPE_KACCESS_ERR_ZERO_MEM_ERR, therefore, the
>> main logic is extracted to copy_page_template.S. In addition, the fixup of
>> MOPS insn is not considered at present.
> 
> Could we not add the exception table entry permanently but ignore the
> exception table entry if it's not on the do_sea() path? That would save
> some code duplication.

The location of the added exception table entry is likely to appear on
the a path, which should not be avoided. What we can do is merge
duplicate code as much as possible, and extract common code into common
files, as we did in this patch.


> 
>> diff --git a/arch/arm64/lib/copy_mc_page.S b/arch/arm64/lib/copy_mc_page.S
>> new file mode 100644
>> index 000000000000..51564828c30c
>> --- /dev/null
>> +++ b/arch/arm64/lib/copy_mc_page.S
>> @@ -0,0 +1,37 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +
>> +#include <linux/linkage.h>
>> +#include <linux/const.h>
>> +#include <asm/assembler.h>
>> +#include <asm/page.h>
>> +#include <asm/cpufeature.h>
>> +#include <asm/alternative.h>
>> +#include <asm/asm-extable.h>
>> +#include <asm/asm-uaccess.h>
>> +
>> +/*
>> + * Copy a page from src to dest (both are page aligned) with memory error safe
>> + *
>> + * Parameters:
>> + *	x0 - dest
>> + *	x1 - src
>> + * Returns:
>> + * 	x0 - Return 0 if copy success, or -EFAULT if anything goes wrong
>> + *	     while copying.
>> + */
>> +	.macro ldp1 reg1, reg2, ptr, val
>> +	KERNEL_MEM_ERR(9998f, ldp \reg1, \reg2, [\ptr, \val])
>> +	.endm
>> +
>> +SYM_FUNC_START(__pi_copy_mc_page)
>> +#include "copy_page_template.S"
>> +
>> +	mov x0, #0
>> +	ret
>> +
>> +9998:	mov x0, #-EFAULT
>> +	ret
>> +
>> +SYM_FUNC_END(__pi_copy_mc_page)
>> +SYM_FUNC_ALIAS(copy_mc_page, __pi_copy_mc_page)
>> +EXPORT_SYMBOL(copy_mc_page)
> [...]
>> diff --git a/arch/arm64/lib/copy_page_template.S b/arch/arm64/lib/copy_page_template.S
>> new file mode 100644
>> index 000000000000..f96c7988c93d
>> --- /dev/null
>> +++ b/arch/arm64/lib/copy_page_template.S
>> @@ -0,0 +1,70 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Copyright (C) 2012 ARM Ltd.
>> + */
>> +
>> +/*
>> + * Copy a page from src to dest (both are page aligned)
>> + *
>> + * Parameters:
>> + *	x0 - dest
>> + *	x1 - src
>> + */
>> +
>> +#ifdef CONFIG_AS_HAS_MOPS
>> +	.arch_extension mops
>> +alternative_if_not ARM64_HAS_MOPS
>> +	b	.Lno_mops
>> +alternative_else_nop_endif
>> +
>> +	mov	x2, #PAGE_SIZE
>> +	cpypwn	[x0]!, [x1]!, x2!
>> +	cpymwn	[x0]!, [x1]!, x2!
>> +	cpyewn	[x0]!, [x1]!, x2!
>> +	ret
>> +.Lno_mops:
>> +#endif
> [...]
> 
> So if we have FEAT_MOPS, the machine check won't work?
> 
> Kristina is going to post MOPS support for the uaccess routines soon.
> You can see how they are wired up and do something similar here.
> 
> But I'd prefer if we had the same code, only the exception table entry
> treated differently. Similarly for the MTE tag copying.

Does MOPS also support features similar to memory error safe? I'll see
how he handles it.

>