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Subject: Re: [PATCH v2 3/4] KVM: SVM: move sev_bind_asid to psp
To:     Mingwei Zhang <mizhang@google.com>,
        Sean Christopherson <seanjc@google.com>
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From:   Brijesh Singh <brijesh.singh@amd.com>
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Date:   Thu, 9 Sep 2021 17:25:25 -0500
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On 9/9/21 4:18 PM, Mingwei Zhang wrote:
>>> Most of the address field in the "struct sev_data_*" are physical
>>> addressess. The userspace will not be able to populate those fields.
>>
>> Yeah, that's my biggest hesitation to using struct sev_data_* in the API, it's
>> both confusing and gross.  But it's also why I think these helpers belong in the
>> PSP driver, KVM should not need to know the "on-the-wire" format for communicating
>> with the PSP.
>>
> 
> Did a simple checking for all struct sev_data_* fields defined in psp-sev.h:

thank you for compiling the list, let me add few more at the end of your 
list (they are part of spec but PSP/KVM does not have support for it).

I am also adding SNP specific so that we get a full picture.

> 
> The average argument is roughly 4 (103/27), detailed data appended at
> last. In addition, I believe the most used commands would be the
> following?
> 
> #data structure name: number of meaningful fields
> sev_data_launch_start: 6
> sev_data_activate: 2
> sev_data_decommission: 1
> sev_data_receive_update_data: 7
> sev_data_send_update_vmsa: 7
> sev_data_launch_measure: 3
> sev_data_launch_finish: 1
> sev_data_deactivate: 1
> 

Once the page copy, and swap in/out is implemented then it will also be 
frequently used.

sev_data_copy: 4
sev_swap_out: 12
sev_swap_in: 7

snp_data_gctx_create: 1
snp_data_activate: 2
snp_data_deactivate: 2
snp_data_decommission: 1
snp_data_launch_start: 6
snp_data_launch_update: 8
snp_data_launch_finish: 6
snp_data_page_move: 4
snp_data_page_swap_out: 8
snp_data_page_swap_in: 8
snp_data_page_reclaim: 2
snp_guest_request: 3
snp_guest_request_ext: 5


> For the above frequently-used command set, the average argument length
> is also around 3-4 (28/8) on average, 2.5 as the median.
> 

It averages around 4-5 (51/11) without snp. The good news is with snp 
the avg is still 4-5 (107/24).

Additionally, we also need to pass the sev->fd in each of these 
functions, which will increase avg to 5-6.


> So, from that perspective, I think we should just remove those
> sev_data data structures in KVM, since it is more clear to read each
> argument.
> 

I believe once we are done with it, will have 5 functions that will need 
 >=8 arguments. I don't know if its acceptable.

> In addition, having to construct each sev_data_* structure in KVM code
> is also a pain and  consumes a lot of irrelevant lines as well.
> 

Maybe I am missing something, aren't those lines will be moved from KVM 
to PSP driver?

I am in full support for restructuring, but lets look at full set of PSP 
APIs before making the final decision.

thanks

> #data structure name: number of meaningful fields
> sev_data_deactivate: 1
> sev_data_decommission: 1
> sev_data_launch_finish: 1
> sev_data_receive_finish: 1
> sev_data_send_cancel: 1
> sev_data_send_finish: 1
> sev_data_activate: 2
> sev_data_download_firmware: 2
> sev_data_get_id: 2
> sev_data_pek_csr: 2
> sev_data_init: 3
> sev_data_launch_measure: 3
> sev_data_launch_update_data: 3
> sev_data_launch_update_vmsa: 3
> sev_data_attestation_report: 4
> sev_data_dbg: 4
> sev_data_guest_status: 4
> sev_data_pdh_cert_export: 4
> sev_data_pek_cert_import: 4
> sev_data_launch_start: 6
> sev_data_receive_start: 6
> sev_data_launch_secret: 7
> sev_data_receive_update_data: 7
> sev_data_receive_update_vmsa: 7
> sev_data_send_update_data: 7
> sev_data_send_update_vmsa: 7
> sev_data_send_start: 10
>