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

From: kirill . shutemov
Date: Sat Oct 14 2023 - 17:01:37 EST


On Fri, Oct 13, 2023 at 04:03:02PM -0700, Compostella, Jeremy wrote:
> "kirill.shutemov@xxxxxxxxxxxxxxx" <kirill.shutemov@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx 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