KVM: MIPS: Use uaccess to read/modify guest instructions

Now that we have GVA page tables, use standard user accesses with page
faults disabled to read & modify guest instructions. This should be more
robust (than the rather dodgy method of accessing guest mapped segments
by just directly addressing them) and will also work with Enhanced
Virtual Addressing (EVA) host kernel configurations where dedicated
instructions are needed for accessing user mode memory.

For simplicity and speed we do this regardless of the guest segment the
address resides in, rather than handling guest KSeg0 specially with
kmap_atomic() as before.

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

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/mips/kvm/trap_emul.c b/arch/mips/kvm/trap_emul.c
index 8bb82eaa4c91..ee8b5ad8c7c5 100644
--- a/arch/mips/kvm/trap_emul.c
+++ b/arch/mips/kvm/trap_emul.c
@@ -12,6 +12,7 @@
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/kvm_host.h>
+#include <linux/uaccess.h>
 #include <linux/vmalloc.h>
 #include <asm/mmu_context.h>
 #include <asm/pgalloc.h>
@@ -798,6 +799,12 @@ static int kvm_trap_emul_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 
 	kvm_trap_emul_vcpu_reenter(run, vcpu);
 
+	/*
+	 * We use user accessors to access guest memory, but we don't want to
+	 * invoke Linux page faulting.
+	 */
+	pagefault_disable();
+
 	/* Disable hardware page table walking while in guest */
 	htw_stop();
 
@@ -823,6 +830,8 @@ static int kvm_trap_emul_vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu)
 
 	htw_start();
 
+	pagefault_enable();
+
 	return r;
 }