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.
