MIPS: KVM: Fix modular KVM under QEMU

commit 797179bc4fe06c89e47a9f36f886f68640b423f8 upstream.

Copy __kvm_mips_vcpu_run() into unmapped memory, so that we can never
get a TLB refill exception in it when KVM is built as a module.

This was observed to happen with the host MIPS kernel running under
QEMU, due to a not entirely transparent optimisation in the QEMU TLB
handling where TLB entries replaced with TLBWR are copied to a separate
part of the TLB array. Code in those pages continue to be executable,
but those mappings persist only until the next ASID switch, even if they
are marked global.

An ASID switch happens in __kvm_mips_vcpu_run() at exception level after
switching to the guest exception base. Subsequent TLB mapped kernel
instructions just prior to switching to the guest trigger a TLB refill
exception, which enters the guest exception handlers without updating
EPC. This appears as a guest triggered TLB refill on a host kernel
mapped (host KSeg2) address, which is not handled correctly as user
(guest) mode accesses to kernel (host) segments always generate address
error exceptions.

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: kvm@vger.kernel.org
Cc: linux-mips@linux-mips.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[james.hogan@imgtec.com: backported for stable 3.14]
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index 4d6fa0bf1305d7376c7ae2ce2201fc412a8791de..883a162083af1fbaa0da483b23acd778ca6385dd 100644 (file)
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -349,6 +349,7 @@ struct kvm_mips_tlb {
 #define KVM_MIPS_GUEST_TLB_SIZE     64
 struct kvm_vcpu_arch {
        void *host_ebase, *guest_ebase;
+       int (*vcpu_run)(struct kvm_run *run, struct kvm_vcpu *vcpu);
        unsigned long host_stack;
        unsigned long host_gp;
 

diff --git a/arch/mips/kvm/kvm_locore.S b/arch/mips/kvm/kvm_locore.S
index ba5ce99c021dcabad85aee540247c0b87f6c9a9c..d1fa2a57218be6e7a8f3de9ab3591703d3e76501 100644 (file)
--- a/arch/mips/kvm/kvm_locore.S
+++ b/arch/mips/kvm/kvm_locore.S
@@ -229,6 +229,7 @@ FEXPORT(__kvm_mips_load_k0k1)
 
        /* Jump to guest */
        eret
+EXPORT(__kvm_mips_vcpu_run_end)
 
 VECTOR(MIPSX(exception), unknown)
 /*

diff --git a/arch/mips/kvm/kvm_mips.c b/arch/mips/kvm/kvm_mips.c
index 7e7de1f2b8edb17ae88337a80e90f65773c9425f..08972791edb4e2be202c729a27c52afd2204353f 100644 (file)
--- a/arch/mips/kvm/kvm_mips.c
+++ b/arch/mips/kvm/kvm_mips.c
@@ -347,6 +347,15 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
        memcpy(gebase + offset, mips32_GuestException,
               mips32_GuestExceptionEnd - mips32_GuestException);
 
+#ifdef MODULE
+       offset += mips32_GuestExceptionEnd - mips32_GuestException;
+       memcpy(gebase + offset, (char *)__kvm_mips_vcpu_run,
+              __kvm_mips_vcpu_run_end - (char *)__kvm_mips_vcpu_run);
+       vcpu->arch.vcpu_run = gebase + offset;
+#else
+       vcpu->arch.vcpu_run = __kvm_mips_vcpu_run;
+#endif
+
        /* Invalidate the icache for these ranges */
        mips32_SyncICache((unsigned long) gebase, ALIGN(size, PAGE_SIZE));
 
@@ -430,7 +439,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 
        kvm_guest_enter();
 
-       r = __kvm_mips_vcpu_run(run, vcpu);
+       r = vcpu->arch.vcpu_run(run, vcpu);
 
        kvm_guest_exit();
        local_irq_enable();

diff --git a/arch/mips/kvm/kvm_mips_int.h b/arch/mips/kvm/kvm_mips_int.h
index 20da7d29eeded15dea951a312999ed3aba30618e..bf41ea36210e17d659ef4b38be8ddbef579724b1 100644 (file)
--- a/arch/mips/kvm/kvm_mips_int.h
+++ b/arch/mips/kvm/kvm_mips_int.h
@@ -27,6 +27,8 @@
 #define MIPS_EXC_MAX                12
 /* XXXSL More to follow */
 
+extern char __kvm_mips_vcpu_run_end[];
+
 #define C_TI        (_ULCAST_(1) << 30)
 
 #define KVM_MIPS_IRQ_DELIVER_ALL_AT_ONCE (0)