On 09/03/2018 03:35 PM, Jan Beulich wrote: >>>> On 03.09.18 at 15:24, <h...@knorrie.org> wrote: >> (XEN) ACPI: LAPIC (acpi_id[0x00] lapic_id[0x00] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x10] lapic_id[0x20] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x08] lapic_id[0x10] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x18] lapic_id[0x30] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x04] lapic_id[0x04] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x14] lapic_id[0x24] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x0c] lapic_id[0x14] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x1c] lapic_id[0x34] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x02] lapic_id[0x02] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x12] lapic_id[0x22] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x0a] lapic_id[0x12] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x1a] lapic_id[0x32] enabled) >> (XEN) ACPI: LAPIC (acpi_id[0x06] lapic_id[0x06] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x16] lapic_id[0x26] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x0e] lapic_id[0x16] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x1e] lapic_id[0x36] disabled) > > These look to be all the primary threads, the last few disabled due > to being absent. > >> (XEN) ACPI: LAPIC (acpi_id[0x01] lapic_id[0x01] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x11] lapic_id[0x21] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x09] lapic_id[0x11] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x19] lapic_id[0x31] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x05] lapic_id[0x05] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x15] lapic_id[0x25] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x0d] lapic_id[0x15] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x1d] lapic_id[0x35] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x03] lapic_id[0x03] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x13] lapic_id[0x23] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x0b] lapic_id[0x13] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x1b] lapic_id[0x33] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x07] lapic_id[0x07] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x17] lapic_id[0x27] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x0f] lapic_id[0x17] disabled) >> (XEN) ACPI: LAPIC (acpi_id[0x1f] lapic_id[0x37] disabled) > > And these are all the secondary threads afaict, which are all > disabled. I'm unconvinced we can assume a system is not using > hyperthreading simply based upon their MADT entries showing all > of them as disabled - what if a HT-enabled CPU was later > hotplugged? > > I would have hoped that the topology related CPUID output > would change when HT is (properly) disabled by the BIOS. > > For the moment I can't see a way around you specifying "smt=0" > on systems like this one.
The actual reason why I started the conversation about it was that for a regular end user, the message telling the user that he has "hardware with SMT/Hyperthreading enabled" is a confusing thing if you just made sure that you have it disabled in the settings. So, alternatively, instead of a technical solution, the warning could be changed to something like "Booted on L1TF-vulnerable hardware and unable to properly detect if SMT/Hyperthreading is enabled or disabled.... Please choose explicit smt setting blah to make sure that it behaves how you want." As a user, that's less confusing, it just tells me that Xen likes me to make explicit what I want. Hans _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
