linux-kernel - Re: [Part2 PATCH v6 13/38] crypto: ccp: Add Secure Encrypted Virtualization (SEV) command support

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Date:   Mon, 23 Oct 2017 14:57:04 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....com, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Gary Hook <gary.hook@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [Part2 PATCH v6 13/38] crypto: ccp: Add Secure Encrypted
 Virtualization (SEV) command support

On 10/23/2017 04:20 AM, Borislav Petkov wrote:
> On Thu, Oct 19, 2017 at 09:33:48PM -0500, Brijesh Singh wrote:
>> +static int __sev_platform_init(struct sev_data_init *data, int *error)
>> +{
>> +	int rc = 0;
>> +
>> +	mutex_lock(&fw_init_mutex);
>> +
>> +	if (!fw_init_count) {
> 
> I still don't like global semaphores. Can you get the status and check
> for PSTATE.INIT state and do the init only if the platform is in
> PSTATE.UNINIT?
> 

Calling PLATFORM_GET_STATUS is not required, we can manage the state 
through a simple ref count variable. Issuing PSP commands will always be 
much more expensive compare to accessing a protected global variable. I 
would prefer to avoid invoking PSP command if possible. Additionally, 
the global semaphore is still needed to serialize the 
sev_platform_init() and sev_platform_shutdown() from multiple processes. 
e.g If process "A" calls sev_platform_init() and if it gets preempted 
due to whatever reason then we don't want another process to issue the 
shutdown command while process "A" is in middle of sev_platform_init().

-Brijesh