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Message-ID: <20231002224752.33qa2lq7q2w4nqws@box>
Date: Tue, 3 Oct 2023 01:47:52 +0300
From: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "mingo@...nel.org" <mingo@...nel.org>,
"Li, Xin3" <xin3.li@...el.com>,
"Compostella, Jeremy" <jeremy.compostella@...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, 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.
I guess we reach the same detect_tme() again via c->c_init() (aka
init_intel()) codepath and get the value right again.
But it seems accidental.
--
Kiryl Shutsemau / Kirill A. Shutemov
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