[PATCH 0/4] MIPS: KVM: Module + non dynamic translating fixes

[PATCH 0/4] MIPS: KVM: Module + non dynamic translating fixes

[James Hogan]

These patches fix a couple of issues I recently spotted when running KVM
under QEMU (i.e. the host MIPS kernel is running under QEMU on a PC).

Patches 1-2: Fix modular KVM broken by QEMU TLB optimisation (Patch 1
marked for stable).

Patches 3-4: Fix cache instruction emulation, exposed by having dynamic
translation of emulated instructions accidentally turned off.

James Hogan (4):
  MIPS: KVM: Fix modular KVM under QEMU
  MIPS: KVM: Include bit 31 in segment matches
  MIPS: KVM: Don't unwind PC when emulating CACHE
  MIPS: KVM: Fix CACHE triggered exception emulation

 arch/mips/include/asm/kvm_host.h |  3 ++-
 arch/mips/kvm/emulate.c          | 21 ++++++++++++++-------
 arch/mips/kvm/interrupt.h        |  1 +
 arch/mips/kvm/locore.S           |  1 +
 arch/mips/kvm/mips.c             | 11 ++++++++++-
 5 files changed, 28 insertions(+), 9 deletions(-)

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
Cc: stable@vger.kernel.org
-- 
2.4.10

[PATCH 1/4] MIPS: KVM: Fix modular KVM under QEMU

[James Hogan]

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
Cc: <stable@vger.kernel.org> # 3.10.x-
---
 arch/mips/include/asm/kvm_host.h |  1 +
 arch/mips/kvm/interrupt.h        |  1 +
 arch/mips/kvm/locore.S           |  1 +
 arch/mips/kvm/mips.c             | 11 ++++++++++-
 4 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index 6733ac575da4..2d5bb133d11a 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -338,6 +338,7 @@ 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/interrupt.h b/arch/mips/kvm/interrupt.h
index 4ab4bdfad703..2143884709e4 100644
--- a/arch/mips/kvm/interrupt.h
+++ b/arch/mips/kvm/interrupt.h
@@ -28,6 +28,7 @@
 #define MIPS_EXC_MAX                12
 /* XXXSL More to follow */
 
+extern char __kvm_mips_vcpu_run_end[];
 extern char mips32_exception[], mips32_exceptionEnd[];
 extern char mips32_GuestException[], mips32_GuestExceptionEnd[];
 
diff --git a/arch/mips/kvm/locore.S b/arch/mips/kvm/locore.S
index 3ef03009de5f..828fcfc1cd7f 100644
--- a/arch/mips/kvm/locore.S
+++ b/arch/mips/kvm/locore.S
@@ -202,6 +202,7 @@ FEXPORT(__kvm_mips_load_k0k1)
 
 	/* Jump to guest */
 	eret
+EXPORT(__kvm_mips_vcpu_run_end)
 
 VECTOR(MIPSX(exception), unknown)
 /* Find out what mode we came from and jump to the proper handler. */
diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index dc052fb5c7a2..44da5259f390 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -315,6 +315,15 @@ 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 */
 	local_flush_icache_range((unsigned long)gebase,
 				(unsigned long)gebase + ALIGN(size, PAGE_SIZE));
@@ -404,7 +413,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
 	/* Disable hardware page table walking while in guest */
 	htw_stop();
 
-	r = __kvm_mips_vcpu_run(run, vcpu);
+	r = vcpu->arch.vcpu_run(run, vcpu);
 
 	/* Re-enable HTW before enabling interrupts */
 	htw_start();
-- 
2.4.10

Re: [PATCH 0/4] MIPS: KVM: Module + non dynamic translating fixes

[Paolo Bonzini]

On 09/06/2016 11:50, James Hogan wrote:
> These patches fix a couple of issues I recently spotted when running KVM
> under QEMU (i.e. the host MIPS kernel is running under QEMU on a PC).
> 
> Patches 1-2: Fix modular KVM broken by QEMU TLB optimisation (Patch 1
> marked for stable).
> 
> Patches 3-4: Fix cache instruction emulation, exposed by having dynamic
> translation of emulated instructions accidentally turned off.
> 
> James Hogan (4):
>   MIPS: KVM: Fix modular KVM under QEMU
>   MIPS: KVM: Include bit 31 in segment matches
>   MIPS: KVM: Don't unwind PC when emulating CACHE
>   MIPS: KVM: Fix CACHE triggered exception emulation
> 
>  arch/mips/include/asm/kvm_host.h |  3 ++-
>  arch/mips/kvm/emulate.c          | 21 ++++++++++++++-------
>  arch/mips/kvm/interrupt.h        |  1 +
>  arch/mips/kvm/locore.S           |  1 +
>  arch/mips/kvm/mips.c             | 11 ++++++++++-
>  5 files changed, 28 insertions(+), 9 deletions(-)
> 
> 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
> Cc: stable@vger.kernel.org
> 

Queued for kvm/master.

Paolo

Re: [PATCH 0/4] MIPS: KVM: Module + non dynamic translating fixes

[Paolo Bonzini]

On 12/06/2016 20:45, Paolo Bonzini wrote:
> 
> 
> On 09/06/2016 11:50, James Hogan wrote:
>> These patches fix a couple of issues I recently spotted when running KVM
>> under QEMU (i.e. the host MIPS kernel is running under QEMU on a PC).
>>
>> Patches 1-2: Fix modular KVM broken by QEMU TLB optimisation (Patch 1
>> marked for stable).
>>
>> Patches 3-4: Fix cache instruction emulation, exposed by having dynamic
>> translation of emulated instructions accidentally turned off.
>>
>> James Hogan (4):
>>   MIPS: KVM: Fix modular KVM under QEMU
>>   MIPS: KVM: Include bit 31 in segment matches
>>   MIPS: KVM: Don't unwind PC when emulating CACHE
>>   MIPS: KVM: Fix CACHE triggered exception emulation
>>
>>  arch/mips/include/asm/kvm_host.h |  3 ++-
>>  arch/mips/kvm/emulate.c          | 21 ++++++++++++++-------
>>  arch/mips/kvm/interrupt.h        |  1 +
>>  arch/mips/kvm/locore.S           |  1 +
>>  arch/mips/kvm/mips.c             | 11 ++++++++++-
>>  5 files changed, 28 insertions(+), 9 deletions(-)
>>
>> 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
>> Cc: stable@vger.kernel.org
>>
> 
> Queued for kvm/master.

... and kvm/next too, since your patches conflict with this one.

Paolo