Re: [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@xxxxxxxxxx
>
> 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