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Date: Thu, 21 Apr 2022 22:33:09 +1200 From: Kai Huang <kai.huang@...el.com> To: Isaku Yamahata <isaku.yamahata@...il.com>, Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com> Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, Hans de Goede <hdegoede@...hat.com>, Mark Gross <mgross@...ux.intel.com>, "H . Peter Anvin" <hpa@...or.com>, "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Tony Luck <tony.luck@...el.com>, Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org Subject: Re: [PATCH v3 4/4] platform/x86: intel_tdx_attest: Add TDX Guest attestation interface driver On Wed, 2022-04-20 at 23:57 -0700, Isaku Yamahata wrote: > On Wed, Apr 20, 2022 at 07:42:06PM -0700, > Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com> wrote: > > > > > > > On 4/20/22 5:11 PM, Kai Huang wrote: > > > On Wed, 2022-04-20 at 16:45 -0700, Sathyanarayanan Kuppuswamy wrote: > > > > If we want to support multiple GetQuote requests in parallel, then we > > > > need some way to uniquely identify the GetQuote requests. So that when > > > > we get completion notification, we can understand which request is > > > > completed. This part is not mentioned/discussed in ABI spec. So we want > > > > to serialize the requests for now. > > > > > > > > > > Yes it's unfortunate that this part (whether concurrent GetQuote requests are > > > supported by TDX architecture) is not explicitly mentioned in GHCI spec. I am > > > fine with only supporting GetQuote requests one by one. AFAICT there's no > > > request to support concurrent GetQuote requests anyway. What concerns me is > > > exactly how explain this. > > > > > > As I said, we have GET_QUOTE_IN_FLIGHT flag now. Theoretically, you can queue > > > multiple GetQuote requests, and when you receive the interrupt, you check which > > > buffer has GET_QUOTE_IN_FLIGHT cleared. That buffer is the one with Quote > > > ready. However I am not 100% sure whether above will always work. Interrupt > > > can get lost when there are multiple Quotes ready in multiple buffer in very > > > short time period, etc? Perhaps Isaku can provide more input here. > > > > Either supported or not, it should be mentioned in the GHCI spec. Currently, > > there are no details related to it. If it is supported, the specification > > should include the protocol to use. > > > > I will check with Isaku about it. > > The spec says that TD can call multiple GetQuote requests in parallel. > > TDG.VP.VMCALL<GetQuote> API allows one TD to issue multiple requests. It's > implementation specific that how many concurrent requests are allowed. The TD > should be able to handle TDG.VP.VMCALL_RETRY if it chooses to issue multiple > requests simultaneously > > As Kai said, there is no requirement for multiple GetQuote in parallel, it's > okay to support only single request at the same time. > > While the status is GET_QUOTE_IN_FLIGHT, VMM owns the shared GPA. The > attestation driver should wait for GET_QUOTE_IN_FLIGHT to be cleared before > sending next request. Sorry I missed this in the spec. Then as I mentioned above, TD should check which buffer has GET_QUOTE_IN_FLIGHT bit cleared to determine which GetQuote request is done? I guess this is the only way. Anyway, supporting single request only is fine to me. Just needs some explanation in comments or commit message. -- Thanks, -Kai
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