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Date:   Fri, 14 Apr 2023 12:40:44 +0800
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Subject: Re: [RFC PATCH V4 06/17] x86/hyperv: decrypt VMBus pages for sev-snp
 enlightened guest
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "luto@kernel.org" <luto@kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
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        "pbonzini@redhat.com" <pbonzini@redhat.com>,
        "jgross@suse.com" <jgross@suse.com>,
        Tianyu Lan <Tianyu.Lan@microsoft.com>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
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References: <20230403174406.4180472-1-ltykernel@gmail.com>
 <20230403174406.4180472-7-ltykernel@gmail.com>
 <BYAPR21MB16882B5A167C985B516B6E5FD79B9@BYAPR21MB1688.namprd21.prod.outlook.com>
From:   Tianyu Lan <ltykernel@gmail.com>
In-Reply-To: <BYAPR21MB16882B5A167C985B516B6E5FD79B9@BYAPR21MB1688.namprd21.prod.outlook.com>
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  On 4/12/2023 10:32 PM, Michael Kelley (LINUX) wrote:
>> @@ -191,6 +222,15 @@ void hv_synic_free(void)
>>   		free_page((unsigned long)hv_cpu->synic_event_page);
>>   		free_page((unsigned long)hv_cpu->synic_message_page);
>>   		free_page((unsigned long)hv_cpu->post_msg_page);
>> +
>> +		if (hv_isolation_type_en_snp()) {
>> +			set_memory_encrypted((unsigned long)
>> +				hv_cpu->synic_message_page, 1);
>> +			set_memory_encrypted((unsigned long)
>> +				hv_cpu->synic_event_page, 1);
>> +			set_memory_encrypted((unsigned long)
>> +				hv_cpu->post_msg_page, 1);
>> +		}
> The re-encryption must be done*before*  pages are freed!
> 
> Furthermore, if the re-encryption fails, we should not free
> the page as it would pollute the free memory pool.  The best
> we can do is leak the memory.  See Patch 5 in Dexuan's
> TDX series, which does the same thing (but still doesn't
> get it quite right, per my comments).
> 

You are right. The order is wrong. we should figure out a right solution 
to handle such case.