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 22:44:24 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Randy Dunlap <rdunlap@...radead.org>
cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>, 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 Tue, 3 Jul 2018, Randy Dunlap wrote:
> 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.

It's a short sentence decribing the function and sentences start usually
with uppercase letters, right?

> I happen to disagree with it.

Then we have to agree that we disagree.

> >> +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'?

Makes is more readable IMO, but I'm not religious about that.

Thanks,

	tglx