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Date:   Tue, 31 Oct 2023 16:52:29 -0700
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Subject: Re: [PATCH v7 06/11] KVM: xen: allow shared_info to be mapped by
 fixed HVA
From:   Sean Christopherson <seanjc@google.com>
To:     Paul Durrant <paul@xen.org>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Paul Durrant <pdurrant@amazon.com>,
        David Woodhouse <dwmw@amazon.co.uk>,
        David Woodhouse <dwmw2@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org
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On Mon, Oct 02, 2023, Paul Durrant wrote:
> NOTE: The change of the kvm_xen_hvm_attr shared_info from struct to union
>       is technically an ABI change but it's entirely compatible with
>       existing users.

It's not an ABI change, is it?  Userspace that picks up the new header might generate
different code on a rebuild, but the actual ABI is unchanged, no?

> @@ -684,6 +692,14 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
>  		r = 0;
>  		break;
>  
> +	case KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA:
> +		if (kvm->arch.xen.shinfo_cache.active)

As requested in previous patches, please explicitly check that the cache is in
the right "mode".

> +			data->u.shared_info.hva = kvm_gpc_hva(&kvm->arch.xen.shinfo_cache);
> +		else
> +			data->u.shared_info.hva = 0;
> +		r = 0;
> +		break;