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

Daniel Vetter
2020-11-30T14:30:35Z

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.

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