linux-kernel - Re: arch/x86/kvm/mmu/paging_tmpl.h:106:24: sparse: sparse: cast truncates bits from constant value (ffffffffff000 becomes fffff000)

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Date:   Wed, 8 Feb 2023 15:11:21 +0800
From:   Yujie Liu <yujie.liu@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     kernel test robot <lkp@...el.com>, <oe-kbuild-all@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: arch/x86/kvm/mmu/paging_tmpl.h:106:24: sparse: sparse: cast
 truncates bits from constant value (ffffffffff000 becomes fffff000)

Hi Sean,

On Tue, Feb 07, 2023 at 11:34:11PM +0000, Sean Christopherson wrote:
> On Tue, Feb 07, 2023, kernel test robot wrote:
> > Hi Sean,
> > 
> > FYI, the error/warning was bisected to this commit, please ignore it if it's irrelevant.
> 
> Is there a way to mark this as "working as intended"?  The truncation is intentional.
> I've been ignoring the reports, but they just keep coming :-)

Sorry for reporting this warning repeatedly. We've added it to the
ignore list for this particular commit.

Best Regards,
Yujie

> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> > head:   d2d11f342b179f1894a901f143ec7c008caba43e
> > commit: 70e41c31bc7776b262cd9f524df3dfc2b5869a0a KVM: x86/mmu: Use common logic for computing the 32/64-bit base PA mask
> > date:   8 months ago
> > config: x86_64-randconfig-s023-20230206 (https://download.01.org/0day-ci/archive/20230207/202302070638.iEBPQ4gL-lkp@intel.com/config)
> > compiler: gcc-11 (Debian 11.3.0-8) 11.3.0
> > reproduce:
> >         # apt-get install sparse
> >         # sparse version: v0.6.4-39-gce1a6720-dirty
> >         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=70e41c31bc7776b262cd9f524df3dfc2b5869a0a
> >         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> >         git fetch --no-tags linus master
> >         git checkout 70e41c31bc7776b262cd9f524df3dfc2b5869a0a
> >         # save the config file
> >         mkdir build_dir && cp config build_dir/.config
> >         make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=x86_64 olddefconfig
> >         make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=x86_64 SHELL=/bin/bash arch/x86/kvm/
> > 
> > If you fix the issue, kindly add following tag where applicable
> > | Reported-by: kernel test robot <lkp@...el.com>
> > 
> > sparse warnings: (new ones prefixed by >>)
> >    arch/x86/kvm/mmu/mmu.c:610:9: sparse: sparse: context imbalance in 'walk_shadow_page_lockless_begin' - different lock contexts for basic block
> >    arch/x86/kvm/mmu/mmu.c: note: in included file (through include/linux/rbtree.h, include/linux/mm_types.h, arch/x86/kvm/irq.h):
> >    include/linux/rcupdate.h:726:9: sparse: sparse: context imbalance in 'walk_shadow_page_lockless_end' - unexpected unlock
> >    arch/x86/kvm/mmu/mmu.c:2550:9: sparse: sparse: context imbalance in 'mmu_try_to_unsync_pages' - different lock contexts for basic block
> >    arch/x86/kvm/mmu/mmu.c: note: in included file:
> > >> arch/x86/kvm/mmu/paging_tmpl.h:106:24: sparse: sparse: cast truncates bits from constant value (ffffffffff000 becomes fffff000)
> >    arch/x86/kvm/mmu/paging_tmpl.h:426:24: sparse: sparse: cast truncates bits from constant value (ffffffffff000 becomes fffff000)
> >    arch/x86/kvm/mmu/mmu.c:4618:57: sparse: sparse: cast truncates bits from constant value (ffffff33 becomes 33)
> >    arch/x86/kvm/mmu/mmu.c:4620:56: sparse: sparse: cast truncates bits from constant value (ffffff0f becomes f)
> >    arch/x86/kvm/mmu/mmu.c:4622:57: sparse: sparse: cast truncates bits from constant value (ffffff55 becomes 55)
> > 
> > vim +106 arch/x86/kvm/mmu/paging_tmpl.h
> > 
> > b3fcdb04a98035 arch/x86/kvm/mmu/paging_tmpl.h Sean Christopherson 2022-06-14  103  
> > e04da980c35d75 arch/x86/kvm/paging_tmpl.h     Joerg Roedel        2009-07-27  104  static gfn_t gpte_to_gfn_lvl(pt_element_t gpte, int lvl)
> > 5fb07ddb183eb4 drivers/kvm/paging_tmpl.h      Avi Kivity          2007-11-21  105  {
> > e04da980c35d75 arch/x86/kvm/paging_tmpl.h     Joerg Roedel        2009-07-27 @106  	return (gpte & PT_LVL_ADDR_MASK(lvl)) >> PAGE_SHIFT;
> > 5fb07ddb183eb4 drivers/kvm/paging_tmpl.h      Avi Kivity          2007-11-21  107  }
> > 5fb07ddb183eb4 drivers/kvm/paging_tmpl.h      Avi Kivity          2007-11-21  108  
> > 
> > :::::: The code at line 106 was first introduced by commit
> > :::::: e04da980c35d75fa050ba4009ad99025432d8d7d KVM: MMU: make page walker aware of mapping levels
> > 
> > :::::: TO: Joerg Roedel <joerg.roedel@....com>
> > :::::: CC: Avi Kivity <avi@...hat.com>
> > 
> > -- 
> > 0-DAY CI Kernel Test Service
> > https://github.com/intel/lkp-tests
>