[SeaBIOS] [PATCH 3/4] support booting with more than 255 CPUs

[Kevin O'Connor]

On Tue, May 10, 2016 at 04:43:33PM +0200, Igor Mammedov wrote:
> SDM[*1] says that if there are CPUs with APIC ID
> greater than 254, BIOS is to pass control to OS
> in x2APIC mode. Use the fact that QEMU passes in
> "etc/max-cpus" max possible "APIC ID + 1" to
> detect need for x2APIC mode. Also instead of
> CMOS_BIOS_SMP_COUNT which is limited to 256 CPUs
> use a new rom file "etc/boot-cpus" that QEMU
> supporting more than 256 CPUs will provide.
> 
> *1) SDM: Volume 3: EXTENDED XAPIC (X2APIC):
>      Initialization by System Software
> 
> Signed-off-by: Igor Mammedov <imammedo at redhat.com>
> ---
>  src/fw/smp.c | 40 ++++++++++++++++++++++++++++++++++------
>  src/x86.h    |  1 +
>  2 files changed, 35 insertions(+), 6 deletions(-)
> 
> diff --git a/src/fw/smp.c b/src/fw/smp.c
> index ad98a5f..18a4c77 100644
> --- a/src/fw/smp.c
> +++ b/src/fw/smp.c
> @@ -19,6 +19,9 @@
>  #define APIC_LINT1   ((u8*)BUILD_APIC_ADDR + 0x360)
>  
>  #define APIC_ENABLED 0x0100
> +#define MSR_IA32_APIC_BASE 0x01B
> +#define MSR_LOCAL_APIC_ID 0x802
> +#define MSR_IA32_APICBASE_EXTD (1ULL << 10) /* Enable x2APIC mode */
>  
>  static struct { u32 index; u64 val; } smp_mtrr[32];
>  static u32 smp_mtrr_count;
> @@ -49,23 +52,46 @@ int apic_id_is_present(u8 apic_id)
>  static int
>  count_cpu(void)
>  {
> +    u32 apic_id;
>      CountCPUs++;
>  
> -    // Track found apic id for use in legacy internal bios tables
>      u32 eax, ebx, ecx, cpuid_features;
>      cpuid(1, &eax, &ebx, &ecx, &cpuid_features);
> -    u8 apic_id = ebx>>24;
> -    FoundAPICIDs[apic_id/32] |= 1 << (apic_id % 32);
> +    apic_id = ebx>>24;
> +    if (MaxCountCPUs < 256) { // xAPIC mode
> +        // Track found apic id for use in legacy internal bios tables
> +        FoundAPICIDs[apic_id/32] |= 1 << (apic_id % 32);
> +    }
> +    if (rdmsr(MSR_IA32_APIC_BASE) & MSR_IA32_APICBASE_EXTD) { // x2APIC mode
> +        apic_id = rdmsr(MSR_LOCAL_APIC_ID);
> +    }
>  
>      return apic_id;
>  }
>  
> +static void
> +handle_x2apic(void)
> +{
> +    if (MaxCountCPUs < 256)
> +        return;
> +
> +    u32 eax, ebx, ecx, edx;
> +    cpuid(1, &eax, &ebx, &ecx, &edx);
> +    if (!(ecx & CPUID_X2APIC))
> +        return;
> +
> +    // switch to x2APIC mode
> +    u64 apic_base = rdmsr(MSR_IA32_APIC_BASE);
> +    wrmsr(MSR_IA32_APIC_BASE, apic_base | MSR_IA32_APICBASE_EXTD);
> +}

Can we integrate handle_x2apic() into count_cpu() as in:

static int
count_cpu(void)
{
    CountCPUs++;

    u32 eax, ebx, ecx, cpuid_features;
    cpuid(1, &eax, &ebx, &ecx, &cpuid_features);
    if (MaxCountCPUs < 256) { // xAPIC mode
        // Track found apic id for use in legacy internal bios tables
        FoundAPICIDs[apic_id/32] |= 1 << (apic_id % 32);
        return ebx>>24;
    }

    // x2APIC mode
    if (!(ecx & CPUID_X2APIC))
        return -1;
    u64 apic_base = rdmsr(MSR_IA32_APIC_BASE);
    wrmsr(MSR_IA32_APIC_BASE, apic_base | MSR_IA32_APICBASE_EXTD);
    return rdmsr(MSR_LOCAL_APIC_ID);
}

count_cpu may be a poor choice of name, but if we could put all the
apic stuff in one function and call it from both handle_smp() and
smp_setup() I think it would make the code a little easier to
understand.

-Kevin