From d5a10b976ecb77fa49b95f3f1016ca2997c122cb Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 15 Dec 2023 15:19:32 +0100 Subject: [PATCH] x86/acpi: Handle bogus MADT APIC tables gracefully The recent fix to ignore invalid x2APIC entries inadvertently broke systems with creative MADT APIC tables. The affected systems have APIC MADT tables where all entries have invalid APIC IDs (0xFF), which means they register exactly zero CPUs. But the condition to ignore the entries of APIC IDs < 255 in the X2APIC MADT table is solely based on the count of MADT APIC table entries. As a consequence, the affected machines enumerate no secondary CPUs at all because the APIC table has entries and therefore the X2APIC table entries with APIC IDs < 255 are ignored. Change the condition so that the APIC table preference for APIC IDs < 255 only becomes effective when the APIC table has valid APIC ID entries. IOW, an APIC table full of invalid APIC IDs is considered to be empty which in consequence enables the X2APIC table entries with a APIC ID < 255 and restores the expected behaviour. Fixes: ec9aedb2aa1a ("x86/acpi: Ignore invalid x2APIC entries") Reported-by: John Sperbeck Reported-by: Andres Freund Signed-off-by: Thomas Gleixner Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/169953729188.3135.6804572126118798018.tip-bot2@tip-bot2 --- arch/x86/kernel/acpi/boot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index 1a0dd80d81ac..85a3ce2a3666 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -293,6 +293,7 @@ acpi_parse_lapic(union acpi_subtable_headers * header, const unsigned long end) processor->processor_id, /* ACPI ID */ processor->lapic_flags & ACPI_MADT_ENABLED); + has_lapic_cpus = true; return 0; } @@ -1134,7 +1135,6 @@ static int __init acpi_parse_madt_lapic_entries(void) if (!count) { count = acpi_table_parse_madt(ACPI_MADT_TYPE_LOCAL_APIC, acpi_parse_lapic, MAX_LOCAL_APIC); - has_lapic_cpus = count > 0; x2count = acpi_table_parse_madt(ACPI_MADT_TYPE_LOCAL_X2APIC, acpi_parse_x2apic, MAX_LOCAL_APIC); }