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Message-ID: <7815a2f0-1ce0-b0d9-6559-a10f13e88a54@intel.com>
Date:   Mon, 12 Dec 2022 08:39:40 -0800
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Subject: Re: [PATCH 2/4] x86/tdx: Use ReportFatalError to report missing
 SEPT_VE_DISABLE
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To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Elena Reshetova <elena.reshetova@intel.com>, x86@kernel.org,
        linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org
References: <20221209132524.20200-1-kirill.shutemov@linux.intel.com>
 <20221209132524.20200-3-kirill.shutemov@linux.intel.com>
 <e79c4b97-5718-9a60-406f-1df994ba089c@linux.intel.com>
 <20221209170647.r32yjyc3hsqtnffo@box.shutemov.name>
 <2e305bb5-9595-3531-6134-24344ff5c797@linux.intel.com>
 <e13331b2-a68c-c823-d02f-ba50949214cb@intel.com>
 <f1937bd1-0400-608d-3cda-b9597c0e4393@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <f1937bd1-0400-608d-3cda-b9597c0e4393@linux.intel.com>
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On 12/12/22 08:37, Sathyanarayanan Kuppuswamy wrote:
> On 12/12/22 8:10 AM, Dave Hansen wrote:
>> On 12/9/22 12:51, Sathyanarayanan Kuppuswamy wrote:
>>>>>> +	while (1) {
>>>>>> +		__tdx_hypercall(&args, 0);
>>>>>> +	}
>>>>> Instead of an infinite loop, I'm wondering if the guest should panic after
>>>>> retrying for few times.
>>>> Hm. What difference would it make?
>>> IIUC, the goal of this patch is to report the fatal error to VMM and panic.
>>> But, if VMM does not terminate the guest as we expect, rather than trying 
>>> continuously, isn't it better to panic ourselves? That way the behavior
>>> will be similar to what we have currently.
>> What does "panic ourselves" mean exactly?  What is the current behavior
>> which that would match?
> I meant directly calling panic(). Before this patch, if the SEPT VE DISABLE
> attribute was not set, we would call panic(). In this patch, we try to report
> the error to VMM and wait for it to terminate the guest in the same case.
> But after reporting the error, if VMM does not terminate the guest as expected,
> I thought instead of retrying continuously, we can call panic() directly after
> some retries. 

Could you explain how panic() is better than retrying?

You might also want to go look at the original changelog for this patch.