linux-kernel - Re: [PATCH 4/9] drivers: hv: Mark shared pages unencrypted in SEV-SNP enlightened guest

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Date:   Thu, 08 Jun 2023 10:54:53 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Tianyu Lan <ltykernel@...il.com>, kys@...rosoft.com,
        haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        daniel.lezcano@...aro.org, arnd@...db.de,
        michael.h.kelley@...rosoft.com
Cc:     Tianyu Lan <tiala@...rosoft.com>, linux-arch@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] drivers: hv: Mark shared pages unencrypted in
 SEV-SNP enlightened guest

Tianyu Lan <ltykernel@...il.com> writes:

> On 6/5/2023 8:54 PM, Vitaly Kuznetsov wrote:
>>> @@ -402,7 +417,14 @@ int hv_common_cpu_die(unsigned int cpu)
>>>   
>>>   	local_irq_restore(flags);
>>>   
>>> -	kfree(mem);
>>> +	if (hv_isolation_type_en_snp()) {
>>> +		ret = set_memory_encrypted((unsigned long)mem, pgcount);
>>> +		if (ret)
>>> +			pr_warn("Hyper-V: Failed to encrypt input arg on cpu%d: %d\n",
>>> +				cpu, ret);
>>> +		/* It's unsafe to free 'mem'. */
>>> +		return 0;
>> Why is it unsafe to free 'mem' if ret == 0? Also, why don't we want to
>> proparate non-zero 'ret' from here to fail CPU offlining?
>> 
>
> Based on Michael's patch the mem will not be freed during cpu offline.
> https://lwn.net/ml/linux-kernel/87cz2j5zrc.fsf@redhat.com/
> So I think it's unnessary to encrypt the mem again here.

Good, you can probably include Michael's patch in your next submission
then (unless it gets merged before that).

-- 
Vitaly