linux-kernel - Re: [PATCH Part2 RFC v4 15/40] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled

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Message-ID: <dfa4ccb5-f85e-6294-6a80-9e4aa6d93c1e@amd.com>
Date:   Fri, 16 Jul 2021 07:55:40 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 15/40] crypto: ccp: Handle the legacy TMR
 allocation when SNP is enabled


On 7/15/21 6:48 PM, Sean Christopherson wrote:
> On Wed, Jul 07, 2021, Brijesh Singh wrote:
>> The behavior and requirement for the SEV-legacy command is altered when
>> the SNP firmware is in the INIT state. See SEV-SNP firmware specification
>> for more details.
>>
>> When SNP is INIT state, all the SEV-legacy commands that cause the
>> firmware to write memory must be in the firmware state. The TMR memory
> It'd be helpful to spell out Trusted Memory Region, I hadn't seen that
> term before and for some reason my brain immediately thought "xAPIC register!".

Noted.


>
>> is allocated by the host but updated by the firmware, so, it must be
>> in the firmware state.  Additionally, the TMR memory must be a 2MB aligned
>> instead of the 1MB, and the TMR length need to be 2MB instead of 1MB.
>> The helper __snp_{alloc,free}_firmware_pages() can be used for allocating
>> and freeing the memory used by the firmware.
> None of this actually states what the patch does, e.g. it's not clear whether
> all allocations are being converted to 2mb or just the SNP.  Looks like it's
> just SNP.  Something like this?
>
>   Allocate the Trusted Memory Region (TMR) as a 2mb sized/aligned region when
>   SNP is enabled to satisfy new requirements for SNP.  Continue allocating a
>   1mb region for !SNP configuration.
>
Only the TMR allocation is converted to use the 2mb when SNP is enabled.


>> While at it, provide API that can be used by others to allocate a page
>> that can be used by the firmware. The immediate user for this API will
>> be the KVM driver. The KVM driver to need to allocate a firmware context
>> page during the guest creation. The context page need to be updated
>> by the firmware. See the SEV-SNP specification for further details.
> ...
>
>> @@ -1153,8 +1269,10 @@ static void sev_firmware_shutdown(struct sev_device *sev)
>>  		/* The TMR area was encrypted, flush it from the cache */
>>  		wbinvd_on_all_cpus();
>>  
>> -		free_pages((unsigned long)sev_es_tmr,
>> -			   get_order(SEV_ES_TMR_SIZE));
>> +
>> +		__snp_free_firmware_pages(virt_to_page(sev_es_tmr),
>> +					  get_order(sev_es_tmr_size),
>> +					  false);
>>  		sev_es_tmr = NULL;
>>  	}
>>  
>> @@ -1204,16 +1322,6 @@ void sev_pci_init(void)
>>  	    sev_update_firmware(sev->dev) == 0)
>>  		sev_get_api_version();
>>  
>> -	/* Obtain the TMR memory area for SEV-ES use */
>> -	tmr_page = alloc_pages(GFP_KERNEL, get_order(SEV_ES_TMR_SIZE));
>> -	if (tmr_page) {
>> -		sev_es_tmr = page_address(tmr_page);
>> -	} else {
>> -		sev_es_tmr = NULL;
>> -		dev_warn(sev->dev,
>> -			 "SEV: TMR allocation failed, SEV-ES support unavailable\n");
>> -	}
>> -
>>  	/*
>>  	 * If boot CPU supports the SNP, then first attempt to initialize
>>  	 * the SNP firmware.
>> @@ -1229,6 +1337,16 @@ void sev_pci_init(void)
>>  		}
>>  	}
>>  
>> +	/* Obtain the TMR memory area for SEV-ES use */
>> +	tmr_page = __snp_alloc_firmware_pages(GFP_KERNEL, get_order(sev_es_tmr_size), false);
>> +	if (tmr_page) {
>> +		sev_es_tmr = page_address(tmr_page);
>> +	} else {
>> +		sev_es_tmr = NULL;
>> +		dev_warn(sev->dev,
>> +			 "SEV: TMR allocation failed, SEV-ES support unavailable\n");
>> +	}
> I think your patch ordering got a bit wonky.  AFAICT, the chunk that added
> sev_snp_init() and friends in the previous patch 14 should have landed above
> the TMR allocation, i.e. the code movement here should be unnecessary.

I was debating about it whether to include all the SNP supports in one
patch or divide it up. If I had included all legacy support new
requirement in the same patch which adds the SNP then it will be a big
patch. I had feeling that others may ask me to split it. So my approach is:

* In the first patch adds SNP support only

* Improve the legacy SEV/ES for the requirement when SNP is enabled.
Once SNP is enabled,  there are two new requirement for the legacy
SEV/ES guests

  1) TMR must be 2mb

  2) The buffer given to the firmware for the write must be in the
firmware state.

I also divided both of the new requirement in separate patches so that
its easy to review.


>
>>  	/* Initialize the platform */
>>  	rc = sev_platform_init(&error);
>>  	if (rc && (error == SEV_RET_SECURE_DATA_INVALID)) {
> ...
>
>> @@ -961,6 +965,13 @@ static inline int snp_guest_dbg_decrypt(struct sev_data_snp_dbg *data, int *erro
>>  	return -ENODEV;
>>  }
>>  
>> +static inline void *snp_alloc_firmware_page(gfp_t mask)
>> +{
>> +	return NULL;
>> +}
>> +
>> +static inline void snp_free_firmware_page(void *addr) { }
> Hmm, I think we should probably bite the bullet and #ifdef and/or stub out large
> swaths of svm/sev.c before adding SNP support.  sev.c is getting quite massive,
> and we're accumulating more and more stubs outside of KVM because its SEV code
> is compiled unconditionally.