linux-kernel - Re: [PATCH] LoongArch: Correct the calculation logic of thread

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Message-ID: <CAEyhmHSqF5DiM2CVyzvAjwTy+KaYAAhwtu2sn1xGWyk4ZF5-bQ@mail.gmail.com>
Date: Wed, 26 Nov 2025 18:06:42 +0800
From: Hengqi Chen <hengqi.chen@...il.com>
To: Qiang Ma <maqianga@...ontech.com>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Huacai Chen <chenhuacai@...nel.org>, kernel@...0n.name
Subject: Re: [PATCH] LoongArch: Correct the calculation logic of thread_count

On Wed, Nov 26, 2025 at 5:47 PM Qiang Ma <maqianga@...ontech.com> wrote:
>
>
> On Wed, Nov 26, 2025 at 10:37 AM Qiang Ma<maqianga@...ontech.com> wrote:
>
> >   For thread_count, the current calculation method has a maximum of 255,
> >   which may not be sufficient in the future. Therefore, we are correcting
> >   it now.
> >
> >   Reference: SMBIOS Specification, 7.5 Processor Information (Type 4)[1]
> >
> >   [1]:https://www.dmtf.org/sites/default/files/standards/documents/DSP0134_3.9.0.pdf
> >
> >   Signed-off-by: Qiang Ma<maqianga@...ontech.com>
> >   ---
> >    arch/loongarch/kernel/setup.c | 9 ++++++++-
> >    1 file changed, 8 insertions(+), 1 deletion(-)
> >
> >   diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
> >   index 25a87378e48e..760f5ce44384 100644
> >   --- a/arch/loongarch/kernel/setup.c
> >   +++ b/arch/loongarch/kernel/setup.c
> >   @@ -56,6 +56,7 @@
> >    #define SMBIOS_FREQLOW_MASK            0xFF
> >    #define SMBIOS_CORE_PACKAGE_OFFSET     0x23
> >    #define SMBIOS_THREAD_PACKAGE_OFFSET   0x25
> >   +#define SMBIOS_THREAD_PACKAGE_2_OFFSET 0x2E
> >    #define LOONGSON_EFI_ENABLE            (1 << 3)
> >
> >    unsigned long fw_arg0, fw_arg1, fw_arg2;
> >   @@ -120,13 +121,19 @@ static void __init parse_cpu_table(const struct dmi_header *dm)
> >    {
> >           long freq_temp = 0;
> >           char *dmi_data = (char *)dm;
> >   +       u8 thread_count;
> >   +       u16 thread_count2;
> >
> >           freq_temp = ((*(dmi_data + SMBIOS_FREQHIGH_OFFSET) << 8) +
> >                           ((*(dmi_data + SMBIOS_FREQLOW_OFFSET)) & SMBIOS_FREQLOW_MASK));
> >           cpu_clock_freq = freq_temp * 1000000;
> >
> >           loongson_sysconf.cpuname = (void *)dmi_string_parse(dm, dmi_data[16]);
> >   -       loongson_sysconf.cores_per_package = *(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> >   +       thread_count = *(dmi_data + SMBIOS_THREAD_PACKAGE_OFFSET);
> >   +       thread_count2 = *(u16 *)(dmi_data + SMBIOS_THREAD_PACKAGE_2_OFFSET);
> >
> > You have `dm->length >= 0x30` below but the memory load already done here.
> After reading thread_count2, it cannot be guaranteed that the data is valid.
>
> 'dm->length >= 0x30' can detect that thread_count2 is an available data,
> right?
>

I mean you should perform the check before doing memory load.

>
> >   +       if (thread_count != 0)
> >   +               loongson_sysconf.cores_per_package = dm->length >= 0x30 && thread_count == 0xFF ?
> >   +                                                    thread_count2 : thread_count;
> >
> >           pr_info("CpuClock = %llu\n", cpu_clock_freq);
> >    }
> >   --
> >   2.20.1