[BACKPORT PATCH 3.10..3.16 1/2] MIPS: KVM: Fix unused variable build warning

[BACKPORT PATCH 3.10..3.16 1/2] MIPS: KVM: Fix unused variable build warning

[James Hogan]

From: Nicholas Mc Guire <hofrat@osadl.org>

commit 5f508c43a7648baa892528922402f1e13f258bd4 upstream.

As kvm_mips_complete_mmio_load() did not yet modify PC at this point
as James Hogans <james.hogan@imgtec.com> explained the curr_pc variable
and the comments along with it can be dropped.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Link: http://lkml.org/lkml/2015/5/8/422
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: kvm@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/9993/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
[james.hogan@imgtec.com: Backport to 3.10..3.16]
Signed-off-by: James Hogan <james.hogan@imgtec.com>
---
 arch/mips/kvm/kvm_mips_emul.c | 6 ------
 1 file changed, 0 insertions(+), 6 deletions(-)

diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
index 1983678883c9..a32e838d9aeb 100644
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -2115,7 +2115,6 @@ kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run)
 {
 	unsigned long *gpr = &vcpu->arch.gprs[vcpu->arch.io_gpr];
 	enum emulation_result er = EMULATE_DONE;
-	unsigned long curr_pc;
 
 	if (run->mmio.len > sizeof(*gpr)) {
 		printk("Bad MMIO length: %d", run->mmio.len);
@@ -2123,11 +2122,6 @@ kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		goto done;
 	}
 
-	/*
-	 * Update PC and hold onto current PC in case there is
-	 * an error and we want to rollback the PC
-	 */
-	curr_pc = vcpu->arch.pc;
 	er = update_pc(vcpu, vcpu->arch.pending_load_cause);
 	if (er == EMULATE_FAIL)
 		return er;
-- 
git-series 0.8.10

[BACKPORT PATCH 3.10..3.16 2/2] KVM: MIPS: Precalculate MMIO load resume PC

[James Hogan]

commit e1e575f6b026734be3b1f075e780e91ab08ca541 upstream.

The advancing of the PC when completing an MMIO load is done before
re-entering the guest, i.e. before restoring the guest ASID. However if
the load is in a branch delay slot it may need to access guest code to
read the prior branch instruction. This isn't safe in TLB mapped code at
the moment, nor in the future when we'll access unmapped guest segments
using direct user accessors too, as it could read the branch from host
user memory instead.

Therefore calculate the resume PC in advance while we're still in the
right context and save it in the new vcpu->arch.io_pc (replacing the no
longer needed vcpu->arch.pending_load_cause), and restore it on MMIO
completion.

Fixes: e685c689f3a8 ("KVM/MIPS32: Privileged instruction/target branch emulation.")
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
Cc: <stable@vger.kernel.org> # 3.10.x-3.16.x: 5f508c43a764: MIPS: KVM: Fix unused variable build warning
Cc: <stable@vger.kernel.org> # 3.10.x-3.16.x
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[james.hogan@imgtec.com: Backport to 3.10..3.16]
Signed-off-by: James Hogan <james.hogan@imgtec.com>
---
 arch/mips/include/asm/kvm_host.h |  7 ++++---
 arch/mips/kvm/kvm_mips_emul.c    | 25 +++++++++++++++----------
 2 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index 5bddbc63fc3b..f8cdc274173a 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -403,7 +403,10 @@ struct kvm_vcpu_arch {
 	/* Host KSEG0 address of the EI/DI offset */
 	void *kseg0_commpage;
 
-	u32 io_gpr;		/* GPR used as IO source/target */
+	/* Resume PC after MMIO completion */
+	unsigned long io_pc;
+	/* GPR used as IO source/target */
+	u32 io_gpr;
 
 	struct hrtimer comparecount_timer;
 	/* Count timer control KVM register */
@@ -425,8 +428,6 @@ struct kvm_vcpu_arch {
 	/* Bitmask of pending exceptions to be cleared */
 	unsigned long pending_exceptions_clr;
 
-	unsigned long pending_load_cause;
-
 	/* Save/Restore the entryhi register when are are preempted/scheduled back in */
 	unsigned long preempt_entryhi;
 
diff --git a/arch/mips/kvm/kvm_mips_emul.c b/arch/mips/kvm/kvm_mips_emul.c
index a32e838d9aeb..4feffc82f39a 100644
--- a/arch/mips/kvm/kvm_mips_emul.c
+++ b/arch/mips/kvm/kvm_mips_emul.c
@@ -1283,6 +1283,7 @@ kvm_mips_emulate_load(uint32_t inst, uint32_t cause,
 		      struct kvm_run *run, struct kvm_vcpu *vcpu)
 {
 	enum emulation_result er = EMULATE_DO_MMIO;
+	unsigned long curr_pc;
 	int32_t op, base, rt, offset;
 	uint32_t bytes;
 
@@ -1291,7 +1292,18 @@ kvm_mips_emulate_load(uint32_t inst, uint32_t cause,
 	offset = inst & 0xffff;
 	op = (inst >> 26) & 0x3f;
 
-	vcpu->arch.pending_load_cause = cause;
+	/*
+	 * Find the resume PC now while we have safe and easy access to the
+	 * prior branch instruction, and save it for
+	 * kvm_mips_complete_mmio_load() to restore later.
+	 */
+	curr_pc = vcpu->arch.pc;
+	er = update_pc(vcpu, cause);
+	if (er == EMULATE_FAIL)
+		return er;
+	vcpu->arch.io_pc = vcpu->arch.pc;
+	vcpu->arch.pc = curr_pc;
+
 	vcpu->arch.io_gpr = rt;
 
 	switch (op) {
@@ -2122,9 +2134,8 @@ kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		goto done;
 	}
 
-	er = update_pc(vcpu, vcpu->arch.pending_load_cause);
-	if (er == EMULATE_FAIL)
-		return er;
+	/* Restore saved resume PC */
+	vcpu->arch.pc = vcpu->arch.io_pc;
 
 	switch (run->mmio.len) {
 	case 4:
@@ -2146,12 +2157,6 @@ kvm_mips_complete_mmio_load(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		break;
 	}
 
-	if (vcpu->arch.pending_load_cause & CAUSEF_BD)
-		kvm_debug
-		    ("[%#lx] Completing %d byte BD Load to gpr %d (0x%08lx) type %d\n",
-		     vcpu->arch.pc, run->mmio.len, vcpu->arch.io_gpr, *gpr,
-		     vcpu->mmio_needed);
-
 done:
 	return er;
 }
-- 
git-series 0.8.10

Re: [BACKPORT PATCH 3.10..3.16 1/2] MIPS: KVM: Fix unused variable build warning

[Willy Tarreau]

Both patches queued for 3.10.y, thanks James!

Willy

Re: [BACKPORT PATCH 3.10..3.16 1/2] MIPS: KVM: Fix unused variable build warning

[Jiri Slaby]

On 11/09/2016, 05:13 PM, James Hogan wrote:
> From: Nicholas Mc Guire <hofrat@osadl.org>
> 
> commit 5f508c43a7648baa892528922402f1e13f258bd4 upstream.

Both applied now to 3.12, albeit the latter didn't apply cleanly.

thanks,
-- 
js
suse labs

Re: [BACKPORT PATCH 3.10..3.16 1/2] MIPS: KVM: Fix unused variable build warning

[James Hogan]

[-- Attachment #1: Type: text/plain, Size: 744 bytes --]

On Wed, Nov 09, 2016 at 10:28:58PM +0100, Jiri Slaby wrote:
> On 11/09/2016, 05:13 PM, James Hogan wrote:
> > From: Nicholas Mc Guire <hofrat@osadl.org>
> > 
> > commit 5f508c43a7648baa892528922402f1e13f258bd4 upstream.
> 
> Both applied now to 3.12, albeit the latter didn't apply cleanly.

/me digs in terminal log

Sorry, I used patch -p1 intentionally when testing 3.12 to try to spot
unclean stable patches, expecting it to reject it, but didn't spot the
fuzz:

$ git show 4.9/kvm/fixes_rc3/stable/3.16 | patch -p1                                                                                 
patching file arch/mips/include/asm/kvm_host.h
Hunk #1 succeeded at 375 with fuzz 2 (offset -28 lines).
...

Thanks
James

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 801 bytes --]