linux-kernel - Re: [PATCH v2 04/12] x86/x86: Add early_is_tdx

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Date:   Fri, 18 Jun 2021 12:14:16 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter H Anvin <hpa@...or.com>,
        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>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 04/12] x86/x86: Add early_is_tdx_guest() interface



On 6/17/21 10:05 AM, Borislav Petkov wrote:
> On Sat, Jun 12, 2021 at 02:04:45PM -0700, Kuppuswamy Sathyanarayanan wrote:
> 
>> Subject: Re: [PATCH v2 04/12] x86/x86: Add early_is_tdx_guest() interface
> 
> Subject prefix should be "x86/tdx:" ofc.

I will fix this in next version.

> 
>> diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c
>> new file mode 100644
>> index 000000000000..ddfa4a6d1939
>> --- /dev/null
>> +++ b/arch/x86/boot/compressed/tdx.c
>> @@ -0,0 +1,28 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * tdx.c - Early boot code for TDX
>> + */
>> +
>> +#include <asm/tdx.h>
> 
> Please no kernel proper includes in the decompressor stage - that thing
> is an include hell mess and needs cleaning up. Use cpuid_count() from
> arch/x86/boot/cpuflags.c by exporting it properly and add the other
> defines here instead of using kernel proper facilities.
> 
> I know, I know, there is other misuse but it has to stop.

I will re-use cpuid_count() from cpuflags.c. But it is missing definition
for cpuid_eax(0). So, I will have to define a new function to handle it.
Hope its alright with you.

> 
>> +static int __ro_after_init tdx_guest = -1;
>> +
>> +static inline bool native_cpuid_has_tdx_guest(void)
> 
> Why is this function prefixed with "native_"?
> 
>> +{
>> +	u32 eax = TDX_CPUID_LEAF_ID, sig[3] = {0};
>> +
>> +	if (native_cpuid_eax(0) < TDX_CPUID_LEAF_ID)
>> +		return false;
>> +
>> +	native_cpuid(&eax, &sig[0], &sig[1], &sig[2]);
>> +
>> +	return !memcmp("IntelTDX    ", sig, 12);
>> +}
>> +
>> +bool early_is_tdx_guest(void)
> 
> So I guess this is going to be used somewhere, because I don't see it.
> Or is it going away in favor of prot_guest_has(PR_GUEST_TDX) ?

It is used for handling TDX specific I/O support in decompressor code.

You can find its usage in https://lore.kernel.org/patchwork/patch/1444186/

May be I should move this patch next to that patch for easy reading.

> 
> This is the problem with sending new versions of patches as a reply to
> the old ones in the patchset: I get confused. Why don't you wait until
> the whole thing has been reviewed and then send a new revision which has
> all the changes and I can find my way in the context?
> 
> And with the amount of changes so far, you should probably send a new
> revision of the initial support set now-ish instead of me reviewing this
> one 'til the end.

I will send the new series with review fixes. Also, since this patch is only
used by I/O support code, I will move this patch to another TDX series which
adds TDX I/O support.

> 
> Thx.
> 

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer