linux-kernel - Re: [PATCH v11 09/13] x86, sgx: basic routines for enclave page cache

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Date:   Mon, 25 Jun 2018 12:01:12 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     x86@...nel.org, platform-driver-x86@...r.kernel.org,
        sean.j.christopherson@...el.com, nhorman@...hat.com,
        npmccallum@...hat.com, Thomas Gleixner <tglx@...utronix.de>,
        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>,
        "open list:INTEL SGX" <intel-sgx-kernel-dev@...ts.01.org>
Subject: Re: [PATCH v11 09/13] x86, sgx: basic routines for enclave page
 cache

On Tue, 2018-06-19 at 08:32 -0700, Dave Hansen wrote:
> > For 32-bit (albeit not supported at this point) it makes sense to always
> > use kmap_atomic_pfn() as the virtua address area is very limited.
> 
> That makes no sense.  32-bit kernels have plenty of virtual address
> space if not using highmem.

AFAIK the vmalloc area is located in the last 128MB that and ioremap()
of EPC would consume a big portion of that.

> > KVM works only with writable MSRs. Driver works both with writable
> > and read-only MSRs.
> 
> Could you help with my confusion by documenting this a bit?

Sure.

/Jarkko