[PATCH v6 00/12] mm/debug_vm_pgtable: Enhancements

[Gavin Shan]

Hi Vineet,

On 8/14/21 5:43 AM, Vineet Gupta wrote:
> On 8/13/21 2:25 AM, Gavin Shan wrote:
>> On 8/12/21 9:11 PM, Anshuman Khandual wrote:
>>> On 8/9/21 2:56 PM, Gavin Shan wrote:
>>>> There are couple of issues with current implementations and this series
>>>> tries to resolve the issues:
>>>>
>>>>    (a) All needed information are scattered in variables, passed to various
>>>>        test functions. The code is organized in pretty much relaxed fashion.
>>>>
>>>>    (b) The page isn't allocated from buddy during page table entry modifying
>>>>        tests. The page can be invalid, conflicting to the implementations
>>>>        of set_xxx_at() on ARM64. The target page is accessed so that the
>>>>        iCache can be flushed when execution permission is given on ARM64.
>>>>        Besides, the target page can be unmapped and accessing to it causes
>>>>        kernel crash.
>>>>
>>>> "struct pgtable_debug_args" is introduced to address issue (a). For issue
>>>> (b), the used page is allocated from buddy in page table entry modifying
>>>> tests. The corresponding tets will be skipped if we fail to allocate the
>>>> (huge) page. For other test cases, the original page around to kernel
>>>> symbol (@start_kernel) is still used.
>>>>
>>>> The patches are organized as below. PATCH[2-10] could be combined to one
>>>> patch, but it will make the review harder:
>>>>
>>>>    PATCH[1] introduces "struct pgtable_debug_args" as place holder of all
>>>>             needed information. With it, the old and new implementation
>>>>             can coexist.
>>>>    PATCH[2-10] uses "struct pgtable_debug_args" in various test functions.
>>>>    PATCH[11] removes the unused code for old implementation.
>>>>    PATCH[12] fixes the issue of corrupted page flag for ARM64
>>>>
>>>> Changelog
>>>> =========
>>>> v6:
>>>>     * Populate saved page table entry pointers after
>>>>       they're allocated in init_args() (Anshuman)
>>>>     * Fix imbalanced preemption count issue by replacing
>>>>       pte_alloc_mmap() with pte_alloc() in init_args() (syzbot)
>>>
>>> + vgupta at kernel.org
> 
> Please also keep linux-snps-arc CC'ed for ARC changes.
> 

Sure.

>>>
>>> Hello Gavin/Vineet,
>>>
>>> This series still need to be tested on ARC ?
>>>
>>
>> Yes, I'm unable to test ARC as it's not supported by QEMU yet.
>> It would great if Vineet can give it a try on ARC :)
> 
> We do have a working QEMU (in the process of being upstreamed) you could try
> https://github.com/foss-for-synopsys-dwc-arc-processors/qemu #master
> 
> Is this code in some shared git repo we can pull - instead of apply 8 files.
> 

Here is repo with v6 series included. Please help to have
a try.

    https://github.com/gwshan/linux  # kvm/arm64_debug

I tried to build the cross-compiler with buildroot with following
2 repos. Unfortunately, none of them worked for me. The QEMU
binary can be built successfully with the provided repo though.


[1] git://github.com/foss-for-synopsys-dwc-arc-processors/buildroot.git
     (branch: master)

     There are build errors after choosing little-endian ARM from
     "make menuconfig"

[2] https://github.com/buildroot/buildroot
     (branch: master)

     The build is successful, but the kernel can't be built because
     of the following errors:
    
     # make ARCH=arc CROSS_COMPILE=arc-linux- axs103_smp_defconfig
     # make -j 40
        :
     LD      vmlinux.o
     arc-linux-ld: error: attempting to link /home/gavin/sandbox/buildroot/buildroot.arc/output/host/lib
     /gcc/arc-buildroot-linux-uclibc/10.2.0/libgcc.a(_muldi3.o) with a binary vmlinux.o of different
     architecture

Thanks,
Gavin