Re: [PATCH] arm64: Support VDSO remapping

[Christopher Covington]

On 12/02/2015 07:19 AM, Will Deacon wrote:
> Hi Christopher,
> 
> On Wed, Nov 25, 2015 at 07:49:29AM -0500, Christopher Covington wrote:
>> Some applications such as Checkpoint/Restore In Userspace (CRIU) remap and
>> unmap the VDSO. Add support for this to the AArch64 kernel by copying in
>> the PowerPC code with slight modifications.
>>
>> Signed-off-by: Christopher Covington <cov@xxxxxxxxxxxxxx>
>> ---
>>  arch/arm64/include/asm/Kbuild          |  1 -
>>  arch/arm64/include/asm/mm-arch-hooks.h | 28 ++++++++++++++++++++++++++++
>>  arch/arm64/include/asm/mmu_context.h   | 23 ++++++++++++++++++++++-
>>  3 files changed, 50 insertions(+), 2 deletions(-)
>>  create mode 100644 arch/arm64/include/asm/mm-arch-hooks.h
>>
>> diff --git a/arch/arm64/include/asm/Kbuild b/arch/arm64/include/asm/Kbuild
>> index 70fd9ff..b112a39 100644
>> --- a/arch/arm64/include/asm/Kbuild
>> +++ b/arch/arm64/include/asm/Kbuild
>> @@ -25,7 +25,6 @@ generic-y += kvm_para.h
>>  generic-y += local.h
>>  generic-y += local64.h
>>  generic-y += mcs_spinlock.h
>> -generic-y += mm-arch-hooks.h
>>  generic-y += mman.h
>>  generic-y += msgbuf.h
>>  generic-y += msi.h
>> diff --git a/arch/arm64/include/asm/mm-arch-hooks.h b/arch/arm64/include/asm/mm-arch-hooks.h
>> new file mode 100644
>> index 0000000..e6923fb
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/mm-arch-hooks.h
>> @@ -0,0 +1,28 @@
>> +/*
>> + * Architecture specific mm hooks
>> + *
>> + * Copyright (C) 2015, IBM Corporation
>> + * Author: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
>> + *
>> + * This program is free software; you can redistribute it and/or modify
>> + * it under the terms of the GNU General Public License version 2 as
>> + * published by the Free Software Foundation.
>> + */
>> +
>> +#ifndef __ASM_MM_ARCH_HOOKS_H
>> +#define __ASM_MM_ARCH_HOOKS_H
>> +
>> +static inline void arch_remap(struct mm_struct *mm,
>> +			      unsigned long old_start, unsigned long old_end,
>> +			      unsigned long new_start, unsigned long new_end)
>> +{
>> +	/*
>> +	 * mremap() doesn't allow moving multiple vmas so we can limit the
>> +	 * check to old_start == vdso_base.
>> +	 */
>> +	if ((void *)old_start == mm->context.vdso)
>> +		mm->context.vdso = (void *)new_start;
>> +}
>> +#define arch_remap arch_remap
>> +
>> +#endif /* __ASM_MM_ARCH_HOOKS_H */
>> diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
>> index 2416578..9fe0773 100644
>> --- a/arch/arm64/include/asm/mmu_context.h
>> +++ b/arch/arm64/include/asm/mmu_context.h
>> @@ -24,7 +24,6 @@
>>  
>>  #include <asm/cacheflush.h>
>>  #include <asm/proc-fns.h>
>> -#include <asm-generic/mm_hooks.h>
>>  #include <asm/cputype.h>
>>  #include <asm/pgtable.h>
>>  
>> @@ -147,4 +146,26 @@ switch_mm(struct mm_struct *prev, struct mm_struct *next,
>>  #define deactivate_mm(tsk,mm)	do { } while (0)
>>  #define activate_mm(prev,next)	switch_mm(prev, next, NULL)
>>  
>> +static inline void arch_dup_mmap(struct mm_struct *oldmm,
>> +				      struct mm_struct *mm)
>> +{
>> +}
>> +
>> +static inline void arch_exit_mmap(struct mm_struct *mm)
>> +{
>> +}
>> +
>> +static inline void arch_unmap(struct mm_struct *mm,
>> +			      struct vm_area_struct *vma,
>> +			      unsigned long start, unsigned long end)
>> +{
>> +	if ((void *)start <= mm->context.vdso && mm->context.vdso < (void *)end)
>> +		mm->context.vdso = NULL;
>> +}
>> +
>> +static inline void arch_bprm_mm_init(struct mm_struct *mm,
>> +				     struct vm_area_struct *vma)
>> +{
>> +}
> 
> This is virtually identical to the PowerPC implementation, afaict. Any
> chance we could move this to core code and define some generic vdso
> accessors for the mm?

I think the same criticism applies to the VDSO code itself, and I'm not
sure how easy it is to provide common VDSO remap/unmap without common
VDSO code. I guess I'll do some investigating when I have then chance.

Thanks,
Christopher Covington

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