[PATCH AUTOSEL for 4.9 09/55] KVM: x86: ioapic: Preserve read-only values in the redirection table

[Sasha Levin]

From: Nikita Leshenko <nikita.leshche...@oracle.com>

[ Upstream commit b200dded0a6974a3b69599832b2203483920ab25 ]

According to 82093AA (IOAPIC) manual, Remote IRR and Delivery Status are
read-only. QEMU implements the bits as RO in commit 479c2a1cb7fb
("ioapic: keep RO bits for IOAPIC entry").

Signed-off-by: Nikita Leshenko <nikita.leshche...@oracle.com>
Reviewed-by: Liran Alon <liran.a...@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com>
Reviewed-by: Wanpeng Li <wanpeng...@hotmail.com>
Reviewed-by: Steve Rutherford <srutherf...@google.com>
Signed-off-by: Radim Krčmář <rkrc...@redhat.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
---
 arch/x86/kvm/ioapic.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index 4b573c8694ac..5f810bb80802 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -278,6 +278,7 @@ static void ioapic_write_indirect(struct kvm_ioapic 
*ioapic, u32 val)
 {
        unsigned index;
        bool mask_before, mask_after;
+       int old_remote_irr, old_delivery_status;
        union kvm_ioapic_redirect_entry *e;
 
        switch (ioapic->ioregsel) {
@@ -300,6 +301,9 @@ static void ioapic_write_indirect(struct kvm_ioapic 
*ioapic, u32 val)
                        return;
                e = &ioapic->redirtbl[index];
                mask_before = e->fields.mask;
+               /* Preserve read-only fields */
+               old_remote_irr = e->fields.remote_irr;
+               old_delivery_status = e->fields.delivery_status;
                if (ioapic->ioregsel & 1) {
                        e->bits &= 0xffffffff;
                        e->bits |= (u64) val << 32;
@@ -307,6 +311,8 @@ static void ioapic_write_indirect(struct kvm_ioapic 
*ioapic, u32 val)
                        e->bits &= ~0xffffffffULL;
                        e->bits |= (u32) val;
                }
+               e->fields.remote_irr = old_remote_irr;
+               e->fields.delivery_status = old_delivery_status;
 
                /*
                 * Some OSes (Linux, Xen) assume that Remote IRR bit will
-- 
2.11.0