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: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index f8cdc274173a204afe89e806e9e04dcf92af0c34..e31b2461cf408d649acff78998b1bca092655b37 100644 (file)
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -378,6 +378,7 @@ 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 fc24acb3a837950d861033eda08605a9d8d38cd3..a397c959a3910fc3f5e24f1b3bac4df1f2715ba8 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 263c6c1c9bbb852bb59ca76ec3d2598689750a48..64f14f6bca5223440b6bc8cbf6cf235ba5e9b610 100644 (file)
--- a/arch/mips/kvm/kvm_mips.c
+++ b/arch/mips/kvm/kvm_mips.c
@@ -342,6 +342,15 @@ 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 */
        flush_icache_range((unsigned long)gebase,
                           (unsigned long)gebase + ALIGN(size, PAGE_SIZE));
@@ -426,7 +435,7 @@ 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)