Re: [PATCH] KVM: x86: fix DR6 delivery for emulated hardware breakpoint

[kbuild test robot]

Hi Paolo,

I love your patch! Yet something to improve:

[auto build test ERROR on kvm/linux-next]
[also build test ERROR on tip/auto-latest linus/master v5.7-rc4 next-20200505]
[cannot apply to linux/master]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Paolo-Bonzini/KVM-x86-fix-DR6-delivery-for-emulated-hardware-breakpoint/20200506-043817
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
config: i386-allyesconfig (attached as .config)
compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <lkp@xxxxxxxxx>

All error/warnings (new ones prefixed by >>):

   arch/x86/kvm/x86.c: In function 'kvm_deliver_exception_payload':
>> arch/x86/kvm/x86.c:472:3: error: implicit declaration of function 'kvm_update_dr6'; did you mean 'kvm_update_cpuid'? [-Werror=implicit-function-declaration]
      kvm_update_dr6(vcpu);
      ^~~~~~~~~~~~~~
      kvm_update_cpuid
   arch/x86/kvm/x86.c: At top level:
>> arch/x86/kvm/x86.c:1071:13: warning: conflicting types for 'kvm_update_dr6'
    static void kvm_update_dr6(struct kvm_vcpu *vcpu)
                ^~~~~~~~~~~~~~
>> arch/x86/kvm/x86.c:1071:13: error: static declaration of 'kvm_update_dr6' follows non-static declaration
   arch/x86/kvm/x86.c:472:3: note: previous implicit declaration of 'kvm_update_dr6' was here
      kvm_update_dr6(vcpu);
      ^~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +472 arch/x86/kvm/x86.c

   432	
   433	void kvm_deliver_exception_payload(struct kvm_vcpu *vcpu)
   434	{
   435		unsigned nr = vcpu->arch.exception.nr;
   436		bool has_payload = vcpu->arch.exception.has_payload;
   437		unsigned long payload = vcpu->arch.exception.payload;
   438	
   439		if (!has_payload)
   440			return;
   441	
   442		switch (nr) {
   443		case DB_VECTOR:
   444			/*
   445			 * "Certain debug exceptions may clear bit 0-3.  The
   446			 * remaining contents of the DR6 register are never
   447			 * cleared by the processor".
   448			 */
   449			vcpu->arch.dr6 &= ~DR_TRAP_BITS;
   450			/*
   451			 * DR6.RTM is set by all #DB exceptions that don't clear it.
   452			 */
   453			vcpu->arch.dr6 |= DR6_RTM;
   454			vcpu->arch.dr6 |= payload;
   455			/*
   456			 * Bit 16 should be set in the payload whenever the #DB
   457			 * exception should clear DR6.RTM. This makes the payload
   458			 * compatible with the pending debug exceptions under VMX.
   459			 * Though not currently documented in the SDM, this also
   460			 * makes the payload compatible with the exit qualification
   461			 * for #DB exceptions under VMX.
   462			 */
   463			vcpu->arch.dr6 ^= payload & DR6_RTM;
   464	
   465			/*
   466			 * The #DB payload is defined as compatible with the 'pending
   467			 * debug exceptions' field under VMX, not DR6. While bit 12 is
   468			 * defined in the 'pending debug exceptions' field (enabled
   469			 * breakpoint), it is reserved and must be zero in DR6.
   470			 */
   471			vcpu->arch.dr6 &= ~BIT(12);
 > 472			kvm_update_dr6(vcpu);
   473			break;
   474		case PF_VECTOR:
   475			vcpu->arch.cr2 = payload;
   476			break;
   477		}
   478	
   479		vcpu->arch.exception.has_payload = false;
   480		vcpu->arch.exception.payload = 0;
   481	}
   482	EXPORT_SYMBOL_GPL(kvm_deliver_exception_payload);
   483	

---
0-DAY CI Kernel Test Service, Intel Corporation
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