Re: [PATCH 2/4] KVM: x86/mmu: Remove redundant is_tdp_mmu_enabled check

[Paolo Bonzini <pbonzini@redhat.com>]

On 18/06/21 09:17, kernel test robot wrote:
> Hi David,
> 
> Thank you for the patch! Yet something to improve:
> 
> [auto build test ERROR on kvm/queue]
> [also build test ERROR on vhost/linux-next v5.13-rc6]
> [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/David-Matlack/KVM-x86-mmu-Remove-redundant-is_tdp_mmu_root-check/20210618-082018
> base:https://git.kernel.org/pub/scm/virt/kvm/kvm.git  queue
> config: i386-randconfig-a016-20210618 (attached as .config)
> compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> reproduce (this is a W=1 build):
>          #https://github.com/0day-ci/linux/commit/6ab060f3cf9061da492b1eb89808eb2da5406781
>          git remote add linux-reviewhttps://github.com/0day-ci/linux
>          git fetch --no-tags linux-review David-Matlack/KVM-x86-mmu-Remove-redundant-is_tdp_mmu_root-check/20210618-082018
>          git checkout 6ab060f3cf9061da492b1eb89808eb2da5406781
>          # save the attached .config to linux build tree
>          make W=1 ARCH=i386
> 
> 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 >>):
> 
>     ld: arch/x86/kvm/mmu/mmu.o: in function `get_mmio_spte':
>>> arch/x86/kvm/mmu/mmu.c:3612: undefined reference to `kvm_tdp_mmu_get_walk'
>     ld: arch/x86/kvm/mmu/mmu.o: in function `direct_page_fault':
>>> arch/x86/kvm/mmu/mmu.c:3830: undefined reference to `kvm_tdp_mmu_map'

Turns out sometimes is_tdp_mmu_root is not inlined after this patch.
Fixed thusly:

--------- 8< -----------
Subject: [PATCH] KVM: x86: Stub out is_tdp_mmu_root on 32-bit hosts

If is_tdp_mmu_root is not inlined, the elimination of TDP MMU calls as dead
code might not work out.  To avoid this, explicitly declare the stubbed
is_tdp_mmu_root on 32-bit hosts.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index fabfea947e46..f6e0667cf4b6 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -85,12 +85,6 @@ bool kvm_mmu_init_tdp_mmu(struct kvm *kvm);
  void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
  static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
  static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; }
-#else
-static inline bool kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return false; }
-static inline void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm) {}
-static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
-static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
-#endif
  
  static inline bool is_tdp_mmu_root(hpa_t hpa)
  {
@@ -105,5 +99,12 @@ static inline bool is_tdp_mmu_root(hpa_t hpa)
  
         return is_tdp_mmu_page(sp) && sp->root_count;
  }
+#else
+static inline bool kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return false; }
+static inline void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm) {}
+static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
+static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
+static inline bool is_tdp_mmu_root(hpa_t hpa) { return false; }
+#endif
  
  #endif /* __KVM_X86_MMU_TDP_MMU_H */