linux-kernel - Re: [PATCH v12 07/13] x86/sgx: data structures for tracking available EPC pages

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Date:   Tue, 3 Jul 2018 13:26:11 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        dave.hansen@...el.com, sean.j.christopherson@...el.com,
        nhorman@...hat.com, npmccallum@...hat.com,
        linux-sgx@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 07/13] x86/sgx: data structures for tracking available
 EPC pages

On 07/03/18 12:46, Thomas Gleixner wrote:
> On Tue, 3 Jul 2018, Jarkko Sakkinen wrote:
> 
>> SGX has a set of data structures to maintain information about the enclaves
>> and their security properties. BIOS reserves a fixed size region of
>> physical memory for these structures by setting Processor Reserved Memory
>> Range Registers (PRMRR). This memory area is called Enclave Page Cache
>> (EPC).
>>
>> This commit adds a database of EPC banks for kernel to easily access the

what kind of database?  How does one query it?

>> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
>> index 2130e639ab49..77b2294fcfb0 100644
>> --- a/arch/x86/include/asm/sgx.h
>> +++ b/arch/x86/include/asm/sgx.h


>> +/**
>> + * sgx_get_page - pin an EPC page
> 
> Description starts with an uppercase letter.

How would someone know that?  It's not documented anywhere.
I happen to disagree with it.


>> +static __init int sgx_page_cache_init(void)
>> +{
>> +	unsigned long size;
>> +	unsigned int eax;
>> +	unsigned int ebx;
>> +	unsigned int ecx;
>> +	unsigned int edx;
>> +	unsigned long pa;
>> +	int i;
>> +	int ret;
> 
> Please aggregate the declarations of the same type. No point in wasting all
> the screen space. And please use 'u32' for ea-dx
> 
>> +
>> +	for (i = 0; i < SGX_MAX_EPC_BANKS; i++) {
>> +		cpuid_count(SGX_CPUID, i + SGX_CPUID_EPC_BANKS, &eax, &ebx,
>> +			    &ecx, &edx);
>> +		if (!(eax & 0xf))
>> +			break;
>> +
>> +		pa = ((u64)(ebx & 0xfffff) << 32) + (u64)(eax & 0xfffff000);
>> +		size = ((u64)(edx & 0xfffff) << 32) + (u64)(ecx & 0xfffff000);
> 
> These magic constants should be 'U', using uppercase 'F' and defines. Plus
> this wants a comment how pa and size are cobbled together from the cpuid
> regs.

Why the uppercase 'F'?

thnx,
-- 
~Randy