Messages in this thread | | | From | "Compostella, Jeremy" <> | Subject | Re: [PATCH v3 1/2] x86/cpu/intel: Fix MTRR verification for TME enabled platforms | Date | Fri, 13 Oct 2023 16:03:02 -0700 |
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"kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.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@linux.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; - arch/x86/kernel/cpu/common.c::arch_cpu_finalize_init() - identify_boot_cpu() - identify_cpu() - get_cpu_address_sizes(c) c->x86_phys_bits = eax & 0xff; - arch/x86/kernel/cpu/intel.c::init_intel() - early_init_intel() - detect_tme() c->x86_phys_bits -= keyid_bits;
> We identify CPU twice: once via early_cpu_init() and the second time via > identify_boot_cpu()/identify_secondary_cpu(). I am talking about > early_cpu_init() codepath. > > It might not matter in practice as of now, because it will get straight > later, but CPU ident code is mess as it is. Let's not make it even worse.
This change is not modifying the CPU indent code, this is just re-ordering detect_tme() call in the intel specifics hook so that the information is available earlier as it is needed by generic_get_mtrr(). This is similar to what is done in arch/x86/kernel/cpu/amd.c.
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