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Message-ID: <e5d163ea-63ca-4c4f-9e69-6d1686be92c3@intel.com>
Date: Fri, 17 May 2024 10:23:23 +1200
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Subject: Re: [PATCH 08/16] KVM: x86/mmu: Bug the VM if kvm_zap_gfn_range() is
 called for TDX
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>, "kvm@vger.kernel.org"
	<kvm@vger.kernel.org>, "pbonzini@redhat.com" <pbonzini@redhat.com>,
	"seanjc@google.com" <seanjc@google.com>
CC: "sagis@google.com" <sagis@google.com>, "dmatlack@google.com"
	<dmatlack@google.com>, "linux-kernel@vger.kernel.org"
	<linux-kernel@vger.kernel.org>, "isaku.yamahata@gmail.com"
	<isaku.yamahata@gmail.com>, "Zhao, Yan Y" <yan.y.zhao@intel.com>, "Aktas,
 Erdem" <erdemaktas@google.com>
References: <20240515005952.3410568-1-rick.p.edgecombe@intel.com>
 <20240515005952.3410568-9-rick.p.edgecombe@intel.com>
 <aa8899fd3bba00720b76836ec4b4eec3347d43dc.camel@intel.com>
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From: "Huang, Kai" <kai.huang@intel.com>
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On 17/05/2024 9:46 am, Edgecombe, Rick P wrote:
> On Tue, 2024-05-14 at 17:59 -0700, Rick Edgecombe wrote:
>>
>> For lack of a better method currently, use kvm_gfn_shared_mask() to
>> determine if private memory cannot be zapped (as in TDX, the only VM type
>> that sets it).
> 
> Trying to replace kvm_gfn_shared_mask() with something appropriate, I saw that
> SNP actually uses this function:
> https://lore.kernel.org/kvm/20240501085210.2213060-12-michael.roth@amd.com/
> 
> So trying to have a helper that says "The VM can't zap and refault in memory at
> will" won't cut it. I guess there would have to be some more specific. I'm
> thinking to just drop this patch instead.

Or KVM_BUG_ON() in the callers by explicitly checking VM type being TDX 
as I mentioned before.

Having such checking in a generic function like this is just dangerous 
and not flexible.

Just my 2 cents, though.