Re: [PATCH 2/3] tools/hvmloader: Replace LAPIC_ID() with cpu_to_apicid[]

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.01.2025 17:33, Alejandro Vallejo wrote:
> Replace uses of the LAPIC_ID() macro with accesses to the
> cpu_to_apicid[] lookup table. This table contains the APIC IDs of each
> vCPU as probed at runtime rather than assuming a predefined relation.
> 
> Moved smp_initialise() ahead of apic_setup() in order to initialise
> cpu_to_apicid ASAP and avoid using it uninitialised. Note that bringing
> up the APs doesn't need the APIC in hvmloader becasue it always runs
> virtualized and uses the PV interface.
> 
> Signed-off-by: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
> ---
> Changes from v7 of the longer topology series:
>   * Removed ASSERT() for the MP tables and merely skipped writing them
>     if any vCPU has an APIC ID >=255.

Throughout the patch I can't anything matching this; ...

> --- a/tools/firmware/hvmloader/config.h
> +++ b/tools/firmware/hvmloader/config.h
> @@ -48,8 +48,9 @@ extern uint8_t ioapic_version;
>  
>  #define IOAPIC_ID           0x01
>  
> +extern uint32_t *cpu_to_apicid;
> +
>  #define LAPIC_BASE_ADDRESS  0xfee00000
> -#define LAPIC_ID(vcpu_id)   ((vcpu_id) * 2)
>  
>  #define PCI_ISA_DEVFN       0x08    /* dev 1, fn 0 */
>  #define PCI_ISA_IRQ_MASK    0x0c20U /* ISA IRQs 5,10,11 are PCI connected */
> --- a/tools/firmware/hvmloader/hvmloader.c
> +++ b/tools/firmware/hvmloader/hvmloader.c
> @@ -224,7 +224,7 @@ static void apic_setup(void)
>  
>      /* 8259A ExtInts are delivered through IOAPIC pin 0 (Virtual Wire Mode). 
> */
>      ioapic_write(0x10, APIC_DM_EXTINT);
> -    ioapic_write(0x11, SET_APIC_ID(LAPIC_ID(0)));
> +    ioapic_write(0x11, SET_APIC_ID(cpu_to_apicid[0]));
>  }
>  
>  struct bios_info {
> @@ -341,11 +341,11 @@ int main(void)
>  
>      printf("CPU speed is %u MHz\n", get_cpu_mhz());
>  
> +    smp_initialise();
> +
>      apic_setup();
>      pci_setup();
>  
> -    smp_initialise();
> -
>      perform_tests();
>  
>      if ( bios->bios_info_setup )
> --- a/tools/firmware/hvmloader/mp_tables.c
> +++ b/tools/firmware/hvmloader/mp_tables.c
> @@ -199,7 +199,7 @@ static void fill_mp_config_table(struct mp_config_table 
> *mpct, int length)
>  static void fill_mp_proc_entry(struct mp_proc_entry *mppe, int vcpu_id)
>  {
>      mppe->type = ENTRY_TYPE_PROCESSOR;
> -    mppe->lapic_id = LAPIC_ID(vcpu_id);
> +    mppe->lapic_id = cpu_to_apicid[vcpu_id];
>      mppe->lapic_version = 0x11;
>      mppe->cpu_flags = CPU_FLAG_ENABLED;
>      if ( vcpu_id == 0 )
> --- a/tools/firmware/hvmloader/util.c
> +++ b/tools/firmware/hvmloader/util.c
> @@ -827,7 +827,7 @@ static void acpi_mem_free(struct acpi_ctxt *ctxt,
>  
>  static uint32_t acpi_lapic_id(unsigned cpu)
>  {
> -    return LAPIC_ID(cpu);
> +    return cpu_to_apicid[cpu];
>  }
>  
>  void hvmloader_acpi_build_tables(struct acpi_config *config,

... no conditional is being added anywhere. What am I missing?

Thing is - this way I'm uncertain whether the wording above is
imprecise, or whether I should really ask that we continue to write all
entries with at most 8-bit-wide APIC IDs, omitting just those with
wider ones.

Jan