linux-kernel - Re: [PATCH v3 2/4] x86/tdx: Add tdx_hcall_get

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Date:   Mon, 18 Apr 2022 22:28:52 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Kai Huang <kai.huang@...el.com>,
        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>
Cc:     "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 2/4] x86/tdx: Add tdx_hcall_get_quote() API support

On 4/18/22 9:40 PM, Kai Huang wrote:
>> Please check the latest 1.0 specification (updated on Feb 2022). It has
>> details about R13 register.
> Thanks.  So it seems GHCI 1.0 has also been updated and it is consistent with
> GHCI 1.5 now.  In this case, why do we still assume 8K shared memory?  Are you
> going to update the driver?
> 

Since the GetQuote spec only requires memory in 4K alignment, we just
went with 8k constant allocation. Since existing users does not
require more than 8k, it works. But I agree that this needs to be
changed.

In next version, I will change the driver to choose the allocation size
based on user space request. Since this change would require us to do
the memory allocation in IOCTL routine (instead of init code), it will
make it slower. But I think this is negligible compared to time it takes
for Quote request. So it should be fine.

> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer