linux-kernel - Re: [PATCH v3 1/2] x86/cpu/intel: Fix MTRR verification for TME enabled platforms

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Message-ID: <20231014210125.iexeacn6p4naw5qz@box.shutemov.name>
Date:   Sun, 15 Oct 2023 00:01:25 +0300
From:   kirill.shutemov@...ux.intel.com
To:     "Compostella, Jeremy" <jeremy.compostella@...el.com>
Cc:     "Huang, Kai" <kai.huang@...el.com>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "Li, Xin3" <xin3.li@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>
Subject: Re: [PATCH v3 1/2] x86/cpu/intel: Fix MTRR verification for TME
 enabled platforms

On Fri, Oct 13, 2023 at 04:03:02PM -0700, Compostella, Jeremy wrote:
> "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com> writes:
> > On Tue, Oct 03, 2023 at 02:06:52AM +0000, Huang, Kai wrote:
> >> On Tue, 2023-10-03 at 01:47 +0300, kirill.shutemov@...ux.intel.com wrote:
> >> > On Fri, Sep 29, 2023 at 09:14:00AM +0000, Huang, Kai wrote:
> >> > > On Thu, 2023-09-28 at 15:30 -0700, Compostella, Jeremy wrote:
> >> > > > On TME enabled platform, BIOS publishes MTRR taking into account Total
> >> > > > Memory Encryption (TME) reserved bits.
> >> > > > 
> >> > > > generic_get_mtrr() performs a sanity check of the MTRRs relying on the
> >> > > > `phys_hi_rsvd' variable which is set using the cpuinfo_x86 structure
> >> > > > `x86_phys_bits' field.  But at the time the generic_get_mtrr()
> >> > > > function is ran the `x86_phys_bits' has not been updated by
> >> > > > detect_tme() when TME is enabled.
> >> > > > 
> >> > > > Since the x86_phys_bits does not reflect yet the real maximal physical
> >> > > > address size yet generic_get_mtrr() complains by logging the following
> >> > > > messages.
> >> > > > 
> >> > > >     mtrr: your BIOS has configured an incorrect mask, fixing it.
> >> > > >     mtrr: your BIOS has configured an incorrect mask, fixing it.
> >> > > >     [...]
> >> > > > 
> >> > > > In such a situation, generic_get_mtrr() returns an incorrect size but
> >> > > > no side effect were observed during our testing.
> >> > > > 
> >> > > > For `x86_phys_bits' to be updated before generic_get_mtrr() runs,
> >> > > > move the detect_tme() call from init_intel() to early_init_intel().
> >> > > 
> >> > > Hi,
> >> > > 
> >> > > This move looks good to me, but +Kirill who is the author of detect_tme() for
> >> > > further comments.
> >> > > 
> >> > > Also I am not sure whether it's worth to consider to move this to
> >> > > get_cpu_address_sizes(), which calculates the virtual/physical address sizes. 
> >> > > Thus it seems anything that can impact physical address size could be put there.
> >> > 
> >> > Actually, I am not sure how this patch works. AFAICS after the patch we
> >> > have the following callchain:
> >> > 
> >> > early_identify_cpu()
> >> >   this_cpu->c_early_init() (which is early_init_init())
> >> >     detect_tme()
> >> >       c->x86_phys_bits -= keyid_bits;
> >> >   get_cpu_address_sizes(c);
> >> >     c->x86_phys_bits = eax & 0xff;
> >> > 
> >> > Looks like get_cpu_address_sizes() would override what detect_tme() does.
> >> 
> >> After this patch, early_identify_cpu() calls get_cpu_address_sizes() first and
> >> then calls c_early_init(), which calls detect_tme().
> >> 
> >> So looks no override.  No?
> 
> No override indeed as get_cpu_address_sizes() is always called before
> early_init_intel or init_intel().
> 
> - init/main.c::start_kernel()
>   - arch/x86/kernel/setup.c::setup_arch()
>     - arch/x86/kernel/cpu/common.c::early_cpu_init()
>       - early_identify_cpu()
>         - get_cpu_address_sizes(c)
>           c->x86_phys_bits = eax & 0xff;
>         - arch/x86/kernel/cpu/intel.c::early_init_intel()
>           - detect_tme()
>             c->x86_phys_bits -= keyid_bits;

Hmm.. Do I read it wrong:

	static void __init early_identify_cpu(struct cpuinfo_x86 *c)
	{
	...
		/* cyrix could have cpuid enabled via c_identify()*/
		if (have_cpuid_p()) {
		...
		        // Here we call early_intel_init()
			if (this_cpu->c_early_init)
				this_cpu->c_early_init(c);
			...
		}

		get_cpu_address_sizes(c);
	...
	}

?

As far as I see get_cpu_address_sizes() called after early_intel_init().

-- 
  Kiryl Shutsemau / Kirill A. Shutemov