linux-kernel - Re: [PATCH] KVM: X86: Declare KVM_CAP_SET_GUEST

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Date:   Tue, 5 May 2020 19:12:37 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Xu <peterx@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH] KVM: X86: Declare KVM_CAP_SET_GUEST_DEBUG properly

On 05/05/20 17:47, Peter Xu wrote:
> KVM_CAP_SET_GUEST_DEBUG should be supported for x86 however it's not declared
> as supported.  My wild guess is that userspaces like QEMU are using "#ifdef
> KVM_CAP_SET_GUEST_DEBUG" to check for the capability instead, but that could be
> wrong because the compilation host may not be the runtime host.
> 
> The userspace might still want to keep the old "#ifdef" though to not break the
> guest debug on old kernels.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
> 
> I also think both ppc and s390 may need similar thing, but I didn't touch them
> yet because of not confident enough to cover all cases.

Indeed, I'll squash this:

diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index e15166b0a16d..ad2f172c26a6 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -521,6 +521,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_IOEVENTFD:
 	case KVM_CAP_DEVICE_CTRL:
 	case KVM_CAP_IMMEDIATE_EXIT:
+	case KVM_CAP_SET_GUEST_DEBUG:
 		r = 1;
 		break;
 	case KVM_CAP_PPC_GUEST_DEBUG_SSTEP:
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 5dcf9ff12828..d05bb040fd42 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -545,6 +545,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_S390_AIS:
 	case KVM_CAP_S390_AIS_MIGRATION:
 	case KVM_CAP_S390_VCPU_RESETS:
+	case KVM_CAP_SET_GUEST_DEBUG:
 		r = 1;
 		break;
 	case KVM_CAP_S390_HPAGE_1M: