Re: [PATCH v7 17/17] mm: add mmu_notifier argument to follow_pfn

Nick Desaulniers
2020-11-30T18:05:35Z

On Mon, Nov 30, 2020 at 6:28 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>
> So I guess kvm platforms that don't set KVM_ARCH_WANT_MMU_NOTIFIER exist,
> and at least on powerpc they're consistent with KVM_CAP_SYNC_MMU
> signalling that the guest pagetables stays in sync automatically with any
> updates. So for that case I guess we could use unsafe_follow_pfn.
>
> But on s390 this seems different: No mmu notifier, but KVM_CAP_SYNC_MMU is
> set. So I guess there's some hardware magic on s390 that I don't know
> about.

+ Vasily + Heiko +s390

>
> Not sure what to do with this now here ...
> -Daniel
>
>
> On Sat, Nov 28, 2020 at 03:10:40AM +0800, kernel test robot wrote:
> > Hi Daniel,
> >
> > I love your patch! Yet something to improve:
> >
> > [auto build test ERROR on linuxtv-media/master]
> > [also build test ERROR on char-misc/char-misc-testing v5.10-rc5]
> > [cannot apply to hnaz-linux-mm/master next-20201127]
> > [If your patch is applied to the wrong git tree, kindly drop us a note.
> > And when submitting patch, we suggest to use '--base' as documented in
> > https://git-scm.com/docs/git-format-patch]
> >
> > url: https://github.com/0day-ci/linux/commits/Daniel-Vetter/follow_pfn-and-other-iomap-races/20201128-004421
> > base: git://linuxtv.org/media_tree.git master
> > config: s390-randconfig-r032-20201127 (attached as .config)
> > compiler: clang version 12.0.0 (https://github.com/llvm/llvm-project f095ac11a9550530a4a54298debb8b04b36422be)
> > reproduce (this is a W=1 build):
> > wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
> > chmod +x ~/bin/make.cross
> > # install s390 cross compiling tool for clang build
> > # apt-get install binutils-s390x-linux-gnu
> > # https://github.com/0day-ci/linux/commit/d76a3489433ce67d45da86aa12953385427f0ac9
> > git remote add linux-review https://github.com/0day-ci/linux
> > git fetch --no-tags linux-review Daniel-Vetter/follow_pfn-and-other-iomap-races/20201128-004421
> > git checkout d76a3489433ce67d45da86aa12953385427f0ac9
> > # save the attached .config to linux build tree
> > COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=s390
> >
> > If you fix the issue, kindly add following tag as appropriate
> > Reported-by: kernel test robot <lkp@intel.com>
> >
> > All errors (new ones prefixed by >>):
> >
> > In file included from arch/s390/include/asm/kvm_para.h:25:
> > In file included from arch/s390/include/asm/diag.h:12:
> > In file included from include/linux/if_ether.h:19:
> > In file included from include/linux/skbuff.h:31:
> > In file included from include/linux/dma-mapping.h:10:
> > In file included from include/linux/scatterlist.h:9:
> > In file included from arch/s390/include/asm/io.h:80:
> > include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
> > ~~~~~~~~~~ ^
> > include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro '__le32_to_cpu'
> > #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
> > ^
> > include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
> > ___constant_swab32(x) : \
> > ^
> > include/uapi/linux/swab.h:21:12: note: expanded from macro '___constant_swab32'
> > (((__u32)(x) & (__u32)0x00ff0000UL) >> 8) | \
> > ^
> > In file included from arch/s390/kvm/../../../virt/kvm/kvm_main.c:18:
> > In file included from include/linux/kvm_host.h:32:
> > In file included from include/linux/kvm_para.h:5:
> > In file included from include/uapi/linux/kvm_para.h:36:
> > In file included from arch/s390/include/asm/kvm_para.h:25:
> > In file included from arch/s390/include/asm/diag.h:12:
> > In file included from include/linux/if_ether.h:19:
> > In file included from include/linux/skbuff.h:31:
> > In file included from include/linux/dma-mapping.h:10:
> > In file included from include/linux/scatterlist.h:9:
> > In file included from arch/s390/include/asm/io.h:80:
> > include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
> > ~~~~~~~~~~ ^
> > include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro '__le32_to_cpu'
> > #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
> > ^
> > include/uapi/linux/swab.h:119:21: note: expanded from macro '__swab32'
> > ___constant_swab32(x) : \
> > ^
> > include/uapi/linux/swab.h:22:12: note: expanded from macro '___constant_swab32'
> > (((__u32)(x) & (__u32)0xff000000UL) >> 24)))
> > ^
> > In file included from arch/s390/kvm/../../../virt/kvm/kvm_main.c:18:
> > In file included from include/linux/kvm_host.h:32:
> > In file included from include/linux/kvm_para.h:5:
> > In file included from include/uapi/linux/kvm_para.h:36:
> > In file included from arch/s390/include/asm/kvm_para.h:25:
> > In file included from arch/s390/include/asm/diag.h:12:
> > In file included from include/linux/if_ether.h:19:
> > In file included from include/linux/skbuff.h:31:
> > In file included from include/linux/dma-mapping.h:10:
> > In file included from include/linux/scatterlist.h:9:
> > In file included from arch/s390/include/asm/io.h:80:
> > include/asm-generic/io.h:490:61: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > val = __le32_to_cpu((__le32 __force)__raw_readl(PCI_IOBASE + addr));
> > ~~~~~~~~~~ ^
> > include/uapi/linux/byteorder/big_endian.h:34:59: note: expanded from macro '__le32_to_cpu'
> > #define __le32_to_cpu(x) __swab32((__force __u32)(__le32)(x))
> > ^
> > include/uapi/linux/swab.h:120:12: note: expanded from macro '__swab32'
> > __fswab32(x))
> > ^
> > In file included from arch/s390/kvm/../../../virt/kvm/kvm_main.c:18:
> > In file included from include/linux/kvm_host.h:32:
> > In file included from include/linux/kvm_para.h:5:
> > In file included from include/uapi/linux/kvm_para.h:36:
> > In file included from arch/s390/include/asm/kvm_para.h:25:
> > In file included from arch/s390/include/asm/diag.h:12:
> > In file included from include/linux/if_ether.h:19:
> > In file included from include/linux/skbuff.h:31:
> > In file included from include/linux/dma-mapping.h:10:
> > In file included from include/linux/scatterlist.h:9:
> > In file included from arch/s390/include/asm/io.h:80:
> > include/asm-generic/io.h:501:33: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > __raw_writeb(value, PCI_IOBASE + addr);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:511:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > __raw_writew((u16 __force)cpu_to_le16(value), PCI_IOBASE + addr);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:521:59: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > __raw_writel((u32 __force)cpu_to_le32(value), PCI_IOBASE + addr);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:609:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > readsb(PCI_IOBASE + addr, buffer, count);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:617:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > readsw(PCI_IOBASE + addr, buffer, count);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:625:20: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > readsl(PCI_IOBASE + addr, buffer, count);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:634:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > writesb(PCI_IOBASE + addr, buffer, count);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:643:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > writesw(PCI_IOBASE + addr, buffer, count);
> > ~~~~~~~~~~ ^
> > include/asm-generic/io.h:652:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> > writesl(PCI_IOBASE + addr, buffer, count);
> > ~~~~~~~~~~ ^
> > >> arch/s390/kvm/../../../virt/kvm/kvm_main.c:1894:40: error: no member named 'mmu_notifier' in 'struct kvm'
> > r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier);
> > ~~~ ^
> > arch/s390/kvm/../../../virt/kvm/kvm_main.c:1909:41: error: no member named 'mmu_notifier' in 'struct kvm'
> > r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier);
> > ~~~ ^
> > 20 warnings and 2 errors generated.
> >
> > vim +1894 arch/s390/kvm/../../../virt/kvm/kvm_main.c
> >
> > 1885
> > 1886 static int hva_to_pfn_remapped(struct kvm *kvm, struct vm_area_struct *vma,
> > 1887 unsigned long addr, bool *async,
> > 1888 bool write_fault, bool *writable,
> > 1889 kvm_pfn_t *p_pfn)
> > 1890 {
> > 1891 unsigned long pfn;
> > 1892 int r;
> > 1893
> > > 1894 r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier);
> > 1895 if (r) {
> > 1896 /*
> > 1897 * get_user_pages fails for VM_IO and VM_PFNMAP vmas and does
> > 1898 * not call the fault handler, so do it here.
> > 1899 */
> > 1900 bool unlocked = false;
> > 1901 r = fixup_user_fault(current->mm, addr,
> > 1902 (write_fault ? FAULT_FLAG_WRITE : 0),
> > 1903 &unlocked);
> > 1904 if (unlocked)
> > 1905 return -EAGAIN;
> > 1906 if (r)
> > 1907 return r;
> > 1908
> > 1909 r = follow_pfn(vma, addr, &pfn, &kvm->mmu_notifier);
> > 1910 if (r)
> > 1911 return r;
> > 1912
> > 1913 }
> > 1914
> > 1915 if (writable)
> > 1916 *writable = true;
> > 1917
> > 1918 /*
> > 1919 * Get a reference here because callers of *hva_to_pfn* and
> > 1920 * *gfn_to_pfn* ultimately call kvm_release_pfn_clean on the
> > 1921 * returned pfn. This is only needed if the VMA has VM_MIXEDMAP
> > 1922 * set, but the kvm_get_pfn/kvm_release_pfn_clean pair will
> > 1923 * simply do nothing for reserved pfns.
> > 1924 *
> > 1925 * Whoever called remap_pfn_range is also going to call e.g.
> > 1926 * unmap_mapping_range before the underlying pages are freed,
> > 1927 * causing a call to our MMU notifier.
> > 1928 */
> > 1929 kvm_get_pfn(pfn);
> > 1930
> > 1931 *p_pfn = pfn;
> > 1932 return 0;
> > 1933 }
> > 1934
> >
> > ---
> > 0-DAY CI Kernel Test Service, Intel Corporation
> > https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch
>
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--
Thanks,
~Nick Desaulniers