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From: Paul Durrant <xadimgnik@gmail.com>
Message-ID: <0f290ba9-4fd1-4986-8562-b90706fd1b5d@xen.org>
Date: Tue, 20 Feb 2024 09:03:30 +0000
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Subject: Re: [PATCH v13 12/21] KVM: x86/xen: allow shared_info to be mapped by
 fixed HVA
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To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
 Christian Borntraeger <borntraeger@linux.ibm.com>,
 Janosch Frank <frankja@linux.ibm.com>,
 Claudio Imbrenda <imbrenda@linux.ibm.com>,
 David Hildenbrand <david@redhat.com>, Heiko Carstens <hca@linux.ibm.com>,
 Vasily Gorbik <gor@linux.ibm.com>, Alexander Gordeev
 <agordeev@linux.ibm.com>, Sven Schnelle <svens@linux.ibm.com>,
 Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
 David Woodhouse <dwmw2@infradead.org>, Shuah Khan <shuah@kernel.org>,
 kvm@vger.kernel.org, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
 linux-kselftest@vger.kernel.org
References: <20240215152916.1158-1-paul@xen.org>
 <20240215152916.1158-13-paul@xen.org> <ZdPNw9evnWw2JzG-@google.com>
Organization: Xen Project
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On 19/02/2024 21:53, Sean Christopherson wrote:
> On Thu, Feb 15, 2024, Paul Durrant wrote:
>> @@ -715,13 +731,23 @@ int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
>>   		break;
>>   
>>   	case KVM_XEN_ATTR_TYPE_SHARED_INFO:
>> -		if (kvm->arch.xen.shinfo_cache.active)
>> +		if (kvm->arch.xen.shinfo_cache.active &&
>> +		    kvm->arch.xen.shinfo_cache.gpa != KVM_XEN_INVALID_GPA)
> 
> This should really use INVALID_GPA when checking internal gpc state.  Mostly to
> help clarify what is/isn't KVM Xen ABI, but also because I don't like the subtle
> assumption that KVM_XEN_INVALID_GPA == INVALID_GPA.
> 

Sorry, yes, that was miss on my part.

> Even better, if we slot in two helpers when the HVA-based GPC support is added,
> then the Xen code doesn't need to to make assumptions about how the GPC code
> manages HVA vs. GPA internally.  E.g. if we ever refactor the code again and use
> a dedicated flag instead of gpc->gpa as the implicit flag.
> 
>    static inline bool kvm_gpc_is_gpa_active(struct gfn_to_pfn_cache *gpc)
>    {
> 	return gpc->active && !kvm_is_error_gpa(gpc->gpa);
>    }
> 
>    static inline bool kvm_gpc_is_hva_active(struct gfn_to_pfn_cache *gpc)
>    {
> 	return gpc->active && kvm_is_error_gpa(gpc->gpa);
>    }

Sure, sounds good to me. I'll add those.