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Re: [PATCH 1/2] x86/ucode: Adjust parse_ucode() to match other list handling


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 26 Feb 2025 15:30:58 +0100
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Wed, 26 Feb 2025 14:31:06 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 25.02.2025 23:29, Andrew Cooper wrote:
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -2721,34 +2721,42 @@ performance.
>     Alternatively, selecting `tsx=1` will re-enable TSX at the users own risk.
>  
>  ### ucode
> -> `= List of [ <integer> | scan=<bool>, nmi=<bool> ]`
> +> `= List of [ <integer>, scan=<bool>, nmi=<bool> ]`

While this makes doc fit present behavior, it is the behavior that is wrong.
It was - afaict - broken by 5ed12565aa32 ("microcode: rendezvous CPUs in NMI
handler and load ucode"). There should not be both an integer and "scan=".
(Really we should have taken measures to stay consistent even if multiple
"ucode=" were on the command line.) You actually say so ...

>      Applicability: x86
>      Default: `scan` is selectable via Kconfig, `nmi=true`
>  
> -Controls for CPU microcode loading. For early loading, this parameter can
> -specify how and where to find the microcode update blob. For late loading,
> -this parameter specifies if the update happens within a NMI handler.
> -
> -'integer' specifies the CPU microcode update blob module index. When 
> positive,
> -this specifies the n-th module (in the GrUB entry, zero based) to be used
> -for updating CPU micrcode. When negative, counting starts at the end of
> -the modules in the GrUB entry (so with the blob commonly being last,
> -one could specify `ucode=-1`). Note that the value of zero is not valid
> -here (entry zero, i.e. the first module, is always the Dom0 kernel
> -image). Note further that use of this option has an unspecified effect
> -when used with xen.efi (there the concept of modules doesn't exist, and
> -the blob gets specified via the `ucode=<filename>` config file/section
> -entry; see [EFI configuration file description](efi.html)).
> -
> -'scan' instructs the hypervisor to scan the multiboot images for an cpio
> -image that contains microcode. Depending on the platform the blob with the
> -microcode in the cpio name space must be:
> -  - on Intel: kernel/x86/microcode/GenuineIntel.bin
> -  - on AMD  : kernel/x86/microcode/AuthenticAMD.bin
> -When using xen.efi, the `ucode=<filename>` config file setting takes
> -precedence over `scan`. The default value for `scan` is set with
> -`CONFIG_UCODE_SCAN_DEFAULT`.
> +Controls for CPU microcode loading.
> +
> +In order to load microcode at boot, Xen needs to find a suitable update
> +amongst the modules provided by the bootloader.  Two kinds of microcode 
> update
> +are supported:
> +
> + 1. Raw microcode containers.  The format of the container is CPU vendor
> +    specific.
> +
> + 2. CPIO archive.  This is Linux's preferred mechanism, and involves having
> +    the raw containers expressed as files
> +    (e.g. `kernel/x86/microcode/{GenuineIntel,AuthenticAMD}.bin`) in a CPIO
> +    archive, typically prepended to the initrd.
> +
> +The `<integer>` and `scan=` options are mutually exclusive and select between
> +these two options.  They are also invalid in EFI boots (see below).

... here.

As to EFI boots: "scan=" ought to be usable there, as long as no "ucode="
was in the xen.efi config file. I think your code is correct in this regard,
it's just the wording here which is too strict.

> --- a/xen/arch/x86/cpu/microcode/core.c
> +++ b/xen/arch/x86/cpu/microcode/core.c
> @@ -113,11 +113,6 @@ void __init microcode_set_module(unsigned int idx)
>      ucode_mod_forced = 1;
>  }
>  
> -/*
> - * The format is '[<integer>|scan=<bool>, nmi=<bool>]'.

While personally I don't mind the removal, I think back at the time it was
specifically asked to (also) put it here.

Jan



 


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