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MIPS: KVM: Restore host EBase from ebase variable 

The host kernel's exception vector base address is currently saved in
the VCPU structure at creation time, and restored on a guest exit.
However it doesn't change and can already be easily accessed from the
'ebase' variable (arch/mips/kernel/traps.c), so drop the host_ebase
member of kvm_vcpu_arch, export the 'ebase' variable to modules and load
from there instead.

This does result in a single extra instruction (lui) on the guest exit
path, but simplifies the code a bit and removes the redundant storage of
the host exception base address.

Credit for the idea goes to Cavium's VZ KVM implementation.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
James Hogan 2016-06-09 14:19:14 +01:00 committed by Paolo Bonzini
parent 26ee17ff71
commit 878edf014e
5 changed files with 3 additions and 6 deletions
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2
arch/mips/include/asm/kvm_host.h
View File

@ -334,7 +334,7 @@ struct kvm_mips_tlb {
#define KVM_MIPS_GUEST_TLB_SIZE 64
struct kvm_vcpu_arch {
void *host_ebase, *guest_ebase;
void *guest_ebase;
int (*vcpu_run)(struct kvm_run *run, struct kvm_vcpu *vcpu);
unsigned long host_stack;
unsigned long host_gp;

1
arch/mips/kernel/asm-offsets.c
View File

@ -355,7 +355,6 @@ void output_kvm_defines(void)
OFFSET(VCPU_RUN, kvm_vcpu, run);
OFFSET(VCPU_HOST_ARCH, kvm_vcpu, arch);
OFFSET(VCPU_HOST_EBASE, kvm_vcpu_arch, host_ebase);
OFFSET(VCPU_GUEST_EBASE, kvm_vcpu_arch, guest_ebase);
OFFSET(VCPU_HOST_STACK, kvm_vcpu_arch, host_stack);

1
arch/mips/kernel/traps.c
View File

@ -1859,6 +1859,7 @@ void __noreturn nmi_exception_handler(struct pt_regs *regs)
#define VECTORSPACING 0x100 /* for EI/VI mode */
unsigned long ebase;
EXPORT_SYMBOL_GPL(ebase);
unsigned long exception_handlers[32];
unsigned long vi_handlers[64];

2
arch/mips/kvm/locore.S
View File

@ -319,7 +319,7 @@ NESTED (MIPSX(GuestException), CALLFRAME_SIZ, ra)
mtc0 k0, CP0_STATUS
ehb
LONG_L k0, VCPU_HOST_EBASE(k1)
LONG_L k0, ebase
mtc0 k0,CP0_EBASE
/*

3
arch/mips/kvm/mips.c
View File

@ -273,9 +273,6 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
else
size = 0x4000;
/* Save Linux EBASE */
vcpu->arch.host_ebase = (void *)read_c0_ebase();
gebase = kzalloc(ALIGN(size, PAGE_SIZE), GFP_KERNEL);
if (!gebase) {