The following commit has been merged into the x86/urgent branch of tip: Commit-ID: cfa16294b1c5b320c0a0e1cac37c784b92366c87 Gitweb: https://git.kernel.org/tip/cfa16294b1c5b320c0a0e1cac37c784b92366c87 Author: Bandan Das <bsd@xxxxxxxxxx> AuthorDate: Mon, 26 Aug 2019 06:15:13 -04:00 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitterDate: Mon, 26 Aug 2019 17:47:24 +02:00 x86/apic: Include the LDR when clearing out APIC registers Although APIC initialization will typically clear out the LDR before setting it, the APIC cleanup code should reset the LDR. This was discovered with a 32-bit KVM guest jumping into a kdump kernel. The stale bits in the LDR triggered a bug in the KVM APIC implementation which caused the destination mapping for VCPUs to be corrupted. Note that this isn't intended to paper over the KVM APIC bug. The kernel has to clear the LDR when resetting the APIC registers except when X2APIC is enabled. This lacks a Fixes tag because missing to clear LDR goes way back into pre git history. Signed-off-by: Bandan Das <bsd@xxxxxxxxxx> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://lkml.kernel.org/r20190826101513.5080-3-bsd@xxxxxxxxxx --- arch/x86/kernel/apic/apic.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c index aa5495d..e75f378 100644 --- a/arch/x86/kernel/apic/apic.c +++ b/arch/x86/kernel/apic/apic.c @@ -1179,6 +1179,10 @@ void clear_local_APIC(void) apic_write(APIC_LVT0, v | APIC_LVT_MASKED); v = apic_read(APIC_LVT1); apic_write(APIC_LVT1, v | APIC_LVT_MASKED); + if (!x2apic_enabled) { + v = apic_read(APIC_LDR) & ~APIC_LDR_MASK; + apic_write(APIC_LDR, v); + } if (maxlvt >= 4) { v = apic_read(APIC_LVTPC); apic_write(APIC_LVTPC, v | APIC_LVT_MASKED);
