The following commit has been merged into the x86/urgent branch of tip:

Commit-ID: 558682b5291937a70748d36fd9ba757fb25b99ae Gitweb: https://git.kernel.org/tip/558682b5291937a70748d36fd9ba757fb25b99ae Author: Bandan Das bsd@redhat.com AuthorDate: Mon, 26 Aug 2019 06:15:13 -04:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Mon, 26 Aug 2019 20:00:57 +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.

[ tglx: Made x2apic_enabled a function call as required ]

Signed-off-by: Bandan Das bsd@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20190826101513.5080-3-bsd@redhat.com

--- 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..dba2828 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);