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SubjectRe: [PATCH 3.3.0-rc3] Fix use-after-free in acpi_map_lsapic
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Len, anyone else, 

Any comments on this one ? This fixes a important bug during cpu hotadd
where the kernel fails to recognize all the newly added cpus.

Thanks,
Alok


On Wed, 2012-02-15 at 16:06 -0800, Petr Vandrovec wrote:
> From: Petr Vandrovec <petr@vmware.com>
>
> When processor is being hot-added to the system, acpi_map_lsapic invokes
> ACPI _MAT method to find APIC ID and flags, verifies that returned structure
> is indeed ACPI's local APIC structure, and that flags contain MADT_ENABLED
> bit. Then saves APIC ID, frees structure - and accesses structure when
> computing arguments for acpi_register_lapic call. Which sometime leads
> to acpi_register_lapic call being made with second argument zero, failing
> to bring processor online with error 'Unable to map lapic to logical cpu
> number'.
>
> As lapic->lapic_flags & ACPI_MADT_ENABLED was already confirmed to be non-zero
> few lines above, we can just pass unconditional ACPI_MADT_ENABLED to the
> acpi_register_lapic.
>
> Thanks, Petr
>
> Signed-off-by: Petr Vandrovec <petr@vmware.com>
> Signed-off-by: Alok Kataria <akataria@vmware.com>
>
>
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index ce664f3..a4a0901 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -650,7 +650,7 @@ static int __cpuinit _acpi_map_lsapic(acpi_handle handle, int *pcpu)
> goto free_tmp_map;
>
> cpumask_copy(tmp_map, cpu_present_mask);
> - acpi_register_lapic(physid, lapic->lapic_flags & ACPI_MADT_ENABLED);
> + acpi_register_lapic(physid, ACPI_MADT_ENABLED);
>
> /*
> * If mp_register_lapic successfully generates a new logical cpu



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