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

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Date:   Sun, 17 Oct 2021 13:35:23 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     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>, thomas.lendacky@....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 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?

>
>> +/*
>> + * tdx_handle_early_io() cannot be re-used in #VE handler for handling
>> + * I/O because the way of handling string I/O is different between
>> + * normal and early I/O case. Also, once trace support is enabled,
>> + * tdx_handle_io() will be extended to use trace calls which is also
>> + * not valid for early I/O cases.
>> + */
>> +static void tdx_handle_io(struct pt_regs *regs, u32 exit_qual)
>> +{
>> +	struct tdx_hypercall_output outh;
>> +	int out, size, port, ret;
>> +	bool string;
>> +	u64 mask;
>> +
>> +	string = VE_IS_IO_STRING(exit_qual);
>> +
>> +	/* I/O strings ops are unrolled at build time. */
> Fancy. The compiler can evaluate sev_key_active() and
> cc_platform_has() at build time?

It is incorrect. I will fix this in next version. How about following
change?

I/O strings are replaced with in/out instructions. If string is reported,
report it with BUG.

>
> Thanks,
>
>          tglx

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer