linux-kernel - Re: [PATCH v3 1/3] crypto: ccp: Add external API interface for PSP module initialization

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Message-ID: <30d6b5d6-d397-490a-afcf-0cae9d6d303c@amd.com>
Date: Fri, 7 Feb 2025 22:52:50 -0600
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Tom Lendacky <thomas.lendacky@....com>, seanjc@...gle.com,
 pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 john.allen@....com, herbert@...dor.apana.org.au, davem@...emloft.net,
 joro@...tes.org, suravee.suthikulpanit@....com, will@...nel.org,
 robin.murphy@....com
Cc: michael.roth@....com, dionnaglaze@...gle.com, nikunj@....com,
 ardb@...nel.org, kevinloughlin@...gle.com, Neeraj.Upadhyay@....com,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-crypto@...r.kernel.org, linux-coco@...ts.linux.dev,
 iommu@...ts.linux.dev
Subject: Re: [PATCH v3 1/3] crypto: ccp: Add external API interface for PSP
 module initialization

Hello Tom,

On 2/7/2025 3:45 PM, Tom Lendacky wrote:
> On 2/3/25 15:56, Ashish Kalra wrote:
>> From: Sean Christopherson <seanjc@...gle.com>
>>
>> KVM is dependent on the PSP SEV driver and PSP SEV driver needs to be
>> loaded before KVM module. In case of module loading any dependent
>> modules are automatically loaded but in case of built-in modules there
>> is no inherent mechanism available to specify dependencies between
>> modules and ensure that any dependent modules are loaded implicitly.
>>
>> Add a new external API interface for PSP module initialization which
>> allows PSP SEV driver to be loaded explicitly if KVM is built-in.
>>
>> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
>> Co-developed-by: Ashish Kalra <ashish.kalra@....com>
>> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
>> ---
>>  drivers/crypto/ccp/sp-dev.c | 14 ++++++++++++++
>>  include/linux/psp-sev.h     |  9 +++++++++
>>  2 files changed, 23 insertions(+)
>>
>> diff --git a/drivers/crypto/ccp/sp-dev.c b/drivers/crypto/ccp/sp-dev.c
>> index 7eb3e4668286..3467f6db4f50 100644
>> --- a/drivers/crypto/ccp/sp-dev.c
>> +++ b/drivers/crypto/ccp/sp-dev.c
>> @@ -19,6 +19,7 @@
>>  #include <linux/types.h>
>>  #include <linux/ccp.h>
>>  
>> +#include "sev-dev.h"
>>  #include "ccp-dev.h"
>>  #include "sp-dev.h"
>>  
>> @@ -253,8 +254,12 @@ struct sp_device *sp_get_psp_master_device(void)
>>  static int __init sp_mod_init(void)
>>  {
>>  #ifdef CONFIG_X86
>> +	static bool initialized;
>>  	int ret;
>>  
>> +	if (initialized)
>> +		return 0;
> 
> Do we need any kind of mutex protection here? Is the init process
> parallelized? We only have one caller today, so probably not a big deal.
> 

Yes the booting will be parallelized, but the main reason we needed to 
explicitly initialize the PSP driver from KVM module load time was that
for the built-in modules case, KVM module was being loaded before the PSP
driver, as per the order of compilation of modules.

So as kvm_amd module will be loading before CCP driver, therefore,
i don't believe kvm module load -> sev_module_init() -> sp_mod_init() can execute
concurrently with CCP module probe -> sp_mod_init(). 

Therefore i believe, the above code in sp_mod_init() should be safe. 

And sev_module_init() is only called in case kvm_amd module is built-in.

Thanks,
Ashish

> If we don't need that:
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> 
> Thanks,
> Tom
> 
>> +
>>  	ret = sp_pci_init();
>>  	if (ret)
>>  		return ret;
>> @@ -263,6 +268,8 @@ static int __init sp_mod_init(void)
>>  	psp_pci_init();
>>  #endif
>>  
>> +	initialized = true;
>> +
>>  	return 0;
>>  #endif
>>  
>> @@ -279,6 +286,13 @@ static int __init sp_mod_init(void)
>>  	return -ENODEV;
>>  }
>>  
>> +#if IS_BUILTIN(CONFIG_KVM_AMD) && IS_ENABLED(CONFIG_KVM_AMD_SEV)
>> +int __init sev_module_init(void)
>> +{
>> +	return sp_mod_init();
>> +}
>> +#endif
>> +
>>  static void __exit sp_mod_exit(void)
>>  {
>>  #ifdef CONFIG_X86
>> diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
>> index 903ddfea8585..f3cad182d4ef 100644
>> --- a/include/linux/psp-sev.h
>> +++ b/include/linux/psp-sev.h
>> @@ -814,6 +814,15 @@ struct sev_data_snp_commit {
>>  
>>  #ifdef CONFIG_CRYPTO_DEV_SP_PSP
>>  
>> +/**
>> + * sev_module_init - perform PSP SEV module initialization
>> + *
>> + * Returns:
>> + * 0 if the PSP module is successfully initialized
>> + * negative value if the PSP module initialization fails
>> + */
>> +int sev_module_init(void);
>> +
>>  /**
>>   * sev_platform_init - perform SEV INIT command
>>   *