Re: [PATCH] powerpc/kvm: support to handle sw breakpoint

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On 17.06.14 13:13, Madhavan Srinivasan wrote:
On Tuesday 17 June 2014 04:38 PM, Alexander Graf wrote:
On 17.06.14 13:07, Madhavan Srinivasan wrote:
On Tuesday 17 June 2014 02:24 PM, Alexander Graf wrote:
On 14.06.14 23:08, Madhavan Srinivasan wrote:
This patch adds kernel side support for software breakpoint.
Design is that, by using an illegal instruction, we trap to hypervisor
via Emulation Assistance interrupt, where we check for the illegal
instruction
and accordingly we return to Host or Guest. Patch mandates use of
"abs" instruction
(primary opcode 31 and extended opcode 360) as sw breakpoint
instruction.
Based on PowerISA v2.01, ABS instruction has been dropped from the
architecture
and treated an illegal instruction.

Signed-off-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxxxxxxx>
---
    arch/powerpc/kvm/book3s.c    |  3 ++-
    arch/powerpc/kvm/book3s_hv.c | 23 +++++++++++++++++++----
    2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kvm/book3s.c b/arch/powerpc/kvm/book3s.c
index c254c27..b40fe5d 100644
--- a/arch/powerpc/kvm/book3s.c
+++ b/arch/powerpc/kvm/book3s.c
@@ -789,7 +789,8 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu
*vcpu,
    int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
                        struct kvm_guest_debug *dbg)
    {
-    return -EINVAL;
+    vcpu->guest_debug = dbg->control;
+    return 0;
    }
      void kvmppc_decrementer_func(unsigned long data)
diff --git a/arch/powerpc/kvm/book3s_hv.c
b/arch/powerpc/kvm/book3s_hv.c
index 7a12edb..688421d 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -67,6 +67,14 @@
    /* Used as a "null" value for timebase values */
    #define TB_NIL    (~(u64)0)
    +/*
+ * SW_BRK_DBG_INT is debug Instruction for supporting Software
Breakpoint.
+ * Instruction mnemonic is ABS, primary opcode is 31 and extended
opcode is 360.
+ * Based on PowerISA v2.01, ABS instruction has been dropped from the
architecture
+ * and treated an illegal instruction.
+ */
+#define SW_BRK_DBG_INT 0x7c0002d0
The instruction we use to trap needs to get exposed to user space via a
ONE_REG property.

Yes. I got to know about that from Bharat (patchset "ppc debug: Add
debug stub support"). I will change it.

Also please make sure to pick an instruction that preferably looks identical regardless of guest endianness. Segher suggested 0x00dddd00. Does that trap properly for you?


Alex

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