Re: [PATCH -next v4 6/7] arm64: add {get, put}_user to machine check safe

[Tong Tiangen]

在 2022/5/13 23:39, Mark Rutland 写道:
> On Wed, Apr 20, 2022 at 03:04:17AM +0000, Tong Tiangen wrote:
> > Add {get, put}_user() to machine check safe.
> >
> > If get/put fail due to hardware memory error, only the relevant processes
> > are affected, so killing the user process and isolate the user page with
> > hardware memory errors is a more reasonable choice than kernel panic.
> >
> > Add new extable type EX_TYPE_UACCESS_MC_ERR_ZERO which can be used for
> > uaccess that can be recovered from hardware memory errors. The difference
> > from EX_TYPE_UACCESS_MC is that this type also sets additional two target
> > register which save error code and value needs to be set zero.
>
> Why does this need to be in any way distinct from the existing
> EX_TYPE_UACCESS_ERR_ZERO ?
>
> Other than the case where we currently (ab)use that for
> copy_{to,from}_kernel_nofault(), where do we *not* want to use
> EX_TYPE_UACCESS_ERR_ZERO and *not* recover from a memory error?
>
> Thanks,
> Mark.

There are some cases (futex/__user_cache_maint()/__user_swpX_asm()) 
using EX_TYPE_UACCESS_ERR_ZERO, for these cases, whether to restore is 
not yet determined, let's discuss in patch 3/7.

Thanks,
Tong.

> > Signed-off-by: Tong Tiangen <tongtiangen@xxxxxxxxxx>
> > ---
> >   arch/arm64/include/asm/asm-extable.h | 14 ++++++++++++++
> >   arch/arm64/include/asm/uaccess.h     |  4 ++--
> >   arch/arm64/mm/extable.c              |  4 ++++
> >   3 files changed, 20 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/asm-extable.h b/arch/arm64/include/asm/asm-extable.h
> > index 75b2c00e9523..80410899a9ad 100644
> > --- a/arch/arm64/include/asm/asm-extable.h
> > +++ b/arch/arm64/include/asm/asm-extable.h
> > @@ -13,6 +13,7 @@
> >   
> >   /* _MC indicates that can fixup from machine check errors */
> >   #define EX_TYPE_UACCESS_MC		5
> > +#define EX_TYPE_UACCESS_MC_ERR_ZERO	6
> >   
> >   #ifdef __ASSEMBLY__
> >   
> > @@ -78,6 +79,15 @@
> >   #define EX_DATA_REG(reg, gpr)						\
> >   	"((.L__gpr_num_" #gpr ") << " __stringify(EX_DATA_REG_##reg##_SHIFT) ")"
> >   
> > +#define _ASM_EXTABLE_UACCESS_MC_ERR_ZERO(insn, fixup, err, zero)		\
> > +	__DEFINE_ASM_GPR_NUMS							\
> > +	__ASM_EXTABLE_RAW(#insn, #fixup,					\
> > +			  __stringify(EX_TYPE_UACCESS_MC_ERR_ZERO),		\
> > +			  "("							\
> > +			    EX_DATA_REG(ERR, err) " | "				\
> > +			    EX_DATA_REG(ZERO, zero)				\
> > +			  ")")
> > +
> >   #define _ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, zero)		\
> >   	__DEFINE_ASM_GPR_NUMS						\
> >   	__ASM_EXTABLE_RAW(#insn, #fixup, 				\
> > @@ -90,6 +100,10 @@
> >   #define _ASM_EXTABLE_UACCESS_ERR(insn, fixup, err)			\
> >   	_ASM_EXTABLE_UACCESS_ERR_ZERO(insn, fixup, err, wzr)
> >   
> > +
> > +#define _ASM_EXTABLE_UACCESS_MC_ERR(insn, fixup, err)			\
> > +	_ASM_EXTABLE_UACCESS_MC_ERR_ZERO(insn, fixup, err, wzr)
> > +
> >   #define EX_DATA_REG_DATA_SHIFT	0
> >   #define EX_DATA_REG_DATA	GENMASK(4, 0)
> >   #define EX_DATA_REG_ADDR_SHIFT	5
> > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> > index e8dce0cc5eaa..e41b47df48b0 100644
> > --- a/arch/arm64/include/asm/uaccess.h
> > +++ b/arch/arm64/include/asm/uaccess.h
> > @@ -236,7 +236,7 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
> >   	asm volatile(							\
> >   	"1:	" load "	" reg "1, [%2]\n"			\
> >   	"2:\n"								\
> > -	_ASM_EXTABLE_UACCESS_ERR_ZERO(1b, 2b, %w0, %w1)			\
> > +	_ASM_EXTABLE_UACCESS_MC_ERR_ZERO(1b, 2b, %w0, %w1)		\
> >   	: "+r" (err), "=&r" (x)						\
> >   	: "r" (addr))
> >   
> > @@ -325,7 +325,7 @@ do {									\
> >   	asm volatile(							\
> >   	"1:	" store "	" reg "1, [%2]\n"			\
> >   	"2:\n"								\
> > -	_ASM_EXTABLE_UACCESS_ERR(1b, 2b, %w0)				\
> > +	_ASM_EXTABLE_UACCESS_MC_ERR(1b, 2b, %w0)			\
> >   	: "+r" (err)							\
> >   	: "r" (x), "r" (addr))
> >   
> > diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> > index 525876c3ebf4..1023ccdb2f89 100644
> > --- a/arch/arm64/mm/extable.c
> > +++ b/arch/arm64/mm/extable.c
> > @@ -88,6 +88,7 @@ bool fixup_exception(struct pt_regs *regs)
> >   	case EX_TYPE_BPF:
> >   		return ex_handler_bpf(ex, regs);
> >   	case EX_TYPE_UACCESS_ERR_ZERO:
> > +	case EX_TYPE_UACCESS_MC_ERR_ZERO:
> >   		return ex_handler_uaccess_err_zero(ex, regs);
> >   	case EX_TYPE_LOAD_UNALIGNED_ZEROPAD:
> >   		return ex_handler_load_unaligned_zeropad(ex, regs);
> > @@ -107,6 +108,9 @@ bool fixup_exception_mc(struct pt_regs *regs)
> >   	switch (ex->type) {
> >   	case EX_TYPE_UACCESS_MC:
> >   		return ex_handler_uaccess_type(ex, regs, FIXUP_TYPE_MC);
> > +	case EX_TYPE_UACCESS_MC_ERR_ZERO:
> > +		return ex_handler_uaccess_err_zero(ex, regs);
> > +
> >   	}
> >   
> >   	return false;
> > --
> > 2.25.1
> .