Re: [PATCH v8 04/11] KVM: x86/mmu: Relax locking for kvm_test_age_gfn and kvm_age_gfn

[kernel test robot <lkp@intel.com>]

Hi James,

kernel test robot noticed the following build warnings:

[auto build test WARNING on a27e0515592ec9ca28e0d027f42568c47b314784]

url:    https://github.com/intel-lab-lkp/linux/commits/James-Houghton/KVM-Remove-kvm_handle_hva_range-helper-functions/20241106-025133
base:   a27e0515592ec9ca28e0d027f42568c47b314784
patch link:    https://lore.kernel.org/r/20241105184333.2305744-5-jthoughton%40google.com
patch subject: [PATCH v8 04/11] KVM: x86/mmu: Relax locking for kvm_test_age_gfn and kvm_age_gfn
config: x86_64-rhel-8.3 (https://download.01.org/0day-ci/archive/20241106/202411061526.RAuCXKJh-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241106/202411061526.RAuCXKJh-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202411061526.RAuCXKJh-lkp@intel.com/

All warnings (new ones prefixed by >>):

   arch/x86/kvm/mmu/tdp_mmu.c: In function 'kvm_tdp_mmu_age_spte':
>> arch/x86/kvm/mmu/tdp_mmu.c:1189:23: warning: ignoring return value of '__tdp_mmu_set_spte_atomic' declared with attribute 'warn_unused_result' [-Wunused-result]
    1189 |                 (void)__tdp_mmu_set_spte_atomic(iter, new_spte);
         |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +1189 arch/x86/kvm/mmu/tdp_mmu.c

  1166	
  1167	/*
  1168	 * Mark the SPTEs range of GFNs [start, end) unaccessed and return non-zero
  1169	 * if any of the GFNs in the range have been accessed.
  1170	 *
  1171	 * No need to mark the corresponding PFN as accessed as this call is coming
  1172	 * from the clear_young() or clear_flush_young() notifier, which uses the
  1173	 * return value to determine if the page has been accessed.
  1174	 */
  1175	static void kvm_tdp_mmu_age_spte(struct tdp_iter *iter)
  1176	{
  1177		u64 new_spte;
  1178	
  1179		if (spte_ad_enabled(iter->old_spte)) {
  1180			iter->old_spte = tdp_mmu_clear_spte_bits_atomic(iter->sptep,
  1181							shadow_accessed_mask);
  1182			new_spte = iter->old_spte & ~shadow_accessed_mask;
  1183		} else {
  1184			new_spte = mark_spte_for_access_track(iter->old_spte);
  1185			/*
  1186			 * It is safe for the following cmpxchg to fail. Leave the
  1187			 * Accessed bit set, as the spte is most likely young anyway.
  1188			 */
> 1189			(void)__tdp_mmu_set_spte_atomic(iter, new_spte);
  1190		}
  1191	
  1192		trace_kvm_tdp_mmu_spte_changed(iter->as_id, iter->gfn, iter->level,
  1193					       iter->old_spte, new_spte);
  1194	}
  1195	

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