linux-kernel - Re: [RFC PATCH V4 06/17] x86/hyperv: decrypt VMBus pages for sev-snp enlightened guest

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Message-ID: <583dd8ba-24f8-c1c6-256b-21a00ae3bd0a@gmail.com>
Date:   Fri, 14 Apr 2023 12:40:44 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "luto@...nel.org" <luto@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
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        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "jgross@...e.com" <jgross@...e.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
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Cc:     "pangupta@....com" <pangupta@....com>,
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        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [RFC PATCH V4 06/17] x86/hyperv: decrypt VMBus pages for sev-snp
 enlightened guest

  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.