linux-kernel - Re: [PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel processors

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Date:   Tue, 23 Jan 2018 18:45:19 +0000
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     David Woodhouse <dwmw@...zon.co.uk>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/5] x86/pti: Do not enable PTI on fixed Intel
 processors

On Tue, 23 Jan 2018 16:52:55 +0000
David Woodhouse <dwmw@...zon.co.uk> wrote:

> When they advertise the IA32_ARCH_CAPABILITIES MSR and it has the RDCL_NO
> bit set, they don't need KPTI either.

This is starting to get messy because we will eventually need to integrate

AMD processors		-	no meltdown but spectre
VIA processors		-	probably no vulnerabilities at
				least on the old ones
Intel with ND set	-	No meltdown
Anybody with no speculation -	No meltdown, no spectre, no id bit



and it expands a lot with all sorts of 32bit processors. Would it make
more sense to make it table driven or do we want a separate function so
we can do:

                if (!in_order_cpu()) {
                }

around the whole lot ? I'm guessing the latter makes sense then
somethhing like this patch I'm running on my old atom widgets in 64bit
mode

static __initdata struct x86_cpu_id cpu_in_order[] = {
        { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CEDARVIEW, X86_FEATURE_ANY },
        { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_CLOVERVIEW, X86_FEATURE_ANY },
        { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_LINCROFT, X86_FEATURE_ANY },
        { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PENWELL, X86_FEATURE_ANY },
        { X86_VENDOR_INTEL, 6, INTEL_FAM6_ATOM_PINEVIEW, X86_FEATURE_ANY },
        {}
};

static int in_order_cpu(void)
{
	/* Processors with CPU id etc */
	if (x86_match_cpu(cpu_in_order))
		return 1;
	/* Other rules here */
	return 0;
}

Alan