linux-kernel - Re: [PATCH v7 05/10] x86/tdx: Handle port I/O

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Message-ID: <51511837-f712-35e2-fdb7-05a2c3f473cb@amd.com>
Date:   Mon, 18 Oct 2021 08:52:30 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 05/10] x86/tdx: Handle port I/O

On 10/17/21 3:35 PM, Sathyanarayanan Kuppuswamy wrote:
> 
> On 10/17/21 12:58 PM, Thomas Gleixner wrote:
>> On Tue, Oct 05 2021 at 13:41, Kuppuswamy Sathyanarayanan wrote:
>>>                                       \
>>>   static inline void outs##bwl(int port, const void *addr, unsigned 
>>> long count) \
>>>   {                                    \
>>> -    if (sev_key_active()) {                        \
>>> +    if (sev_key_active() ||                        \
>>> +        cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) {        \
>> Instead of adding an extra check, can you please replace that
>> sev_key_active() with cc_platform_has() completely?
> 
> Yes. sev_key_active() can be removed and replaced with
> cc_platform_has().
> 
> Thomas Lendacky also proposed to introduce as common
> static key which can be set by both AMD SEV and TDX code.
> 
> @Thomas Lendacky, any comments?

Either way works for me.

For the cc_platform_has() path, you will need to update the 
amd_cc_platform_has() to return true for CC_ATTR_GUEST_UNROLL_STRING_IO 
for SEV only, i.e.:

	case CC_ATTR_GUEST_UNROLL_STRING_IO:
		return (sev_status & MSR_AMD64_SEV_ENABLED) &&
		       !(sev_status & MSR_AMD64_SEV_ES_ENABLED);

Thanks,
Tom