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Message-ID: <0da734f3-5743-3df3-3f90-d92e5bd585ce@huawei.com>
Date: Sat, 18 Jun 2022 16:42:06 +0800
From: Tong Tiangen <tongtiangen@...wei.com>
To: Mark Rutland <mark.rutland@....com>
CC: James Morse <james.morse@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
"Ingo Molnar" <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Robin Murphy <robin.murphy@....com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"Catalin Marinas" <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
"Alexander Viro" <viro@...iv.linux.org.uk>,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>, <x86@...nel.org>,
"H . Peter Anvin" <hpa@...or.com>, <linuxppc-dev@...ts.ozlabs.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Xie XiuQi <xiexiuqi@...wei.com>,
Guohanjun <guohanjun@...wei.com>
Subject: Re: [PATCH -next v5 2/8] arm64: extable: make uaaccess helper use
extable type EX_TYPE_UACCESS_ERR_ZERO
在 2022/6/18 11:26, Tong Tiangen 写道:
>
>
> 在 2022/6/17 16:24, Mark Rutland 写道:
>> On Sat, May 28, 2022 at 06:50:50AM +0000, Tong Tiangen wrote:
>>> Currnetly, the extable type used by __arch_copy_from/to_user() is
>>> EX_TYPE_FIXUP. In fact, It is more clearly to use meaningful
>>> EX_TYPE_UACCESS_*.
>>>
>>> Suggested-by: Mark Rutland <mark.rutland@....com>
>>> Signed-off-by: Tong Tiangen <tongtiangen@...wei.com>
>>> ---
>>> arch/arm64/include/asm/asm-extable.h | 8 ++++++++
>>> arch/arm64/include/asm/asm-uaccess.h | 12 ++++++------
>>> 2 files changed, 14 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/asm-extable.h
>>> b/arch/arm64/include/asm/asm-extable.h
>>> index 56ebe183e78b..9c94ac1f082c 100644
>>> --- a/arch/arm64/include/asm/asm-extable.h
>>> +++ b/arch/arm64/include/asm/asm-extable.h
>>> @@ -28,6 +28,14 @@
>>> __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_FIXUP, 0)
>>> .endm
>>> +/*
>>> + * Create an exception table entry for uaccess `insn`, which will
>>> branch to `fixup`
>>> + * when an unhandled fault is taken.
>>> + * ex->data = ~0 means both reg_err and reg_zero is set to wzr(x31).
>>> + */
>>> + .macro _asm_extable_uaccess, insn, fixup
>>> + __ASM_EXTABLE_RAW(\insn, \fixup, EX_TYPE_UACCESS_ERR_ZERO, ~0)
>>> + .endm
>>
>> I'm not too keen on using `~0` here, since that also sets other bits
>> in the
>> data field, and its somewhat opaque.
>>
>> How painful is it to generate the data fields as with the C version of
>> this
>> macro, so that we can pass in wzr explciitly for the two sub-fields?
>>
>> Other than that, this looks good to me.
>>
>> Thanks,
>> Mark.
>
> ok, will fix next version.
>
> Thanks,
> Tong.
I tried to using data filelds as with C version, but here assembly code
we can not using operator such as << and |, if we use lsl and orr
instructions, the gpr will be occupied.
So how about using 0x3ff directly here? it means err register and zero
register both set to x31.
Thanks,
Tong.
>
>>
>>> /*
>>> * Create an exception table entry for `insn` if `fixup` is
>>> provided. Otherwise
>>> * do nothing.
>>> diff --git a/arch/arm64/include/asm/asm-uaccess.h
>>> b/arch/arm64/include/asm/asm-uaccess.h
>>> index 0557af834e03..75b211c98dea 100644
>>> --- a/arch/arm64/include/asm/asm-uaccess.h
>>> +++ b/arch/arm64/include/asm/asm-uaccess.h
>>> @@ -61,7 +61,7 @@ alternative_else_nop_endif
>>> #define USER(l, x...) \
>>> 9999: x; \
>>> - _asm_extable 9999b, l
>>> + _asm_extable_uaccess 9999b, l
>>> /*
>>> * Generate the assembly for LDTR/STTR with exception table entries.
>>> @@ -73,8 +73,8 @@ alternative_else_nop_endif
>>> 8889: ldtr \reg2, [\addr, #8];
>>> add \addr, \addr, \post_inc;
>>> - _asm_extable 8888b,\l;
>>> - _asm_extable 8889b,\l;
>>> + _asm_extable_uaccess 8888b, \l;
>>> + _asm_extable_uaccess 8889b, \l;
>>> .endm
>>> .macro user_stp l, reg1, reg2, addr, post_inc
>>> @@ -82,14 +82,14 @@ alternative_else_nop_endif
>>> 8889: sttr \reg2, [\addr, #8];
>>> add \addr, \addr, \post_inc;
>>> - _asm_extable 8888b,\l;
>>> - _asm_extable 8889b,\l;
>>> + _asm_extable_uaccess 8888b,\l;
>>> + _asm_extable_uaccess 8889b,\l;
>>> .endm
>>> .macro user_ldst l, inst, reg, addr, post_inc
>>> 8888: \inst \reg, [\addr];
>>> add \addr, \addr, \post_inc;
>>> - _asm_extable 8888b,\l;
>>> + _asm_extable_uaccess 8888b, \l;
>>> .endm
>>> #endif
>>> --
>>> 2.25.1
>>>
>> .
>
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