> -----Original Message----- > From: Alexander Graf [mailto:agraf@xxxxxxx] > Sent: Thursday, April 04, 2013 6:55 PM > To: Bhushan Bharat-R65777 > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; kvm-ppc@xxxxxxxxxxxxxxx; > Wood Scott-B07421; Bhushan Bharat-R65777 > Subject: Re: [PATCH] bookehv: Handle debug exception on guest exit > > > On 20.03.2013, at 18:45, Bharat Bhushan wrote: > > > EPCR.DUVD controls whether the debug events can come in hypervisor > > mode or not. When KVM guest is using the debug resource then we do not > > want debug events to be captured in guest entry/exit path. So we set > > EPCR.DUVD when entering and clears EPCR.DUVD when exiting from guest. > > > > Debug instruction complete is a post-completion debug exception but > > debug event gets posted on the basis of MSR before the instruction is > > executed. Now if the instruction switches the context from guest mode > > (MSR.GS = 1) to hypervisor mode (MSR.GS = 0) then the xSRR0 points to > > first instruction of KVM handler and xSRR1 points that MSR.GS is clear > > (hypervisor context). Now as xSRR1.GS is used to decide whether KVM > > handler will be invoked to handle the exception or host host kernel > > debug handler will be invoked to handle the exception. > > This leads to host kernel debug handler handling the exception which > > should either be handled by KVM. > > > > This is tested on e500mc in 32 bit mode > > > > Signed-off-by: Bharat Bhushan <bharat.bhushan@xxxxxxxxxxxxx> > > --- > > v0: > > - Do not apply this change for debug_crit as we do not know those chips have > issue or not. > > - corrected 64bit case branching > > > > arch/powerpc/kernel/exceptions-64e.S | 29 ++++++++++++++++++++++++++++- > > arch/powerpc/kernel/head_booke.h | 26 ++++++++++++++++++++++++++ > > 2 files changed, 54 insertions(+), 1 deletions(-) > > > > diff --git a/arch/powerpc/kernel/exceptions-64e.S > > b/arch/powerpc/kernel/exceptions-64e.S > > index 4684e33..8b26294 100644 > > --- a/arch/powerpc/kernel/exceptions-64e.S > > +++ b/arch/powerpc/kernel/exceptions-64e.S > > @@ -516,6 +516,33 @@ kernel_dbg_exc: > > andis. r15,r14,DBSR_IC@h > > beq+ 1f > > > > +#ifdef CONFIG_KVM_BOOKE_HV > > + /* > > + * EPCR.DUVD controls whether the debug events can come in > > + * hypervisor mode or not. When KVM guest is using the debug > > + * resource then we do not want debug events to be captured > > + * in guest entry/exit path. So we set EPCR.DUVD when entering > > + * and clears EPCR.DUVD when exiting from guest. > > + * Debug instruction complete is a post-completion debug > > + * exception but debug event gets posted on the basis of MSR > > + * before the instruction is executed. Now if the instruction > > + * switches the context from guest mode (MSR.GS = 1) to hypervisor > > + * mode (MSR.GS = 0) then the xSRR0 points to first instruction of > > Can't we just execute that code path with MSR.DE=0? Single stepping uses DBCR0.IC (instruction complete). Can you describe how MSR.DE = 0 will work? > > > Alex > > > + * KVM handler and xSRR1 points that MSR.GS is clear > > + * (hypervisor context). Now as xSRR1.GS is used to decide whether > > + * KVM handler will be invoked to handle the exception or host > > + * host kernel debug handler will be invoked to handle the exception. > > + * This leads to host kernel debug handler handling the exception > > + * which should either be handled by KVM. > > + */ > > + mfspr r10, SPRN_EPCR > > + andis. r10,r10,SPRN_EPCR_DUVD@h > > + beq+ 2f > > + > > + andis. r10,r9,MSR_GS@h > > + beq+ 3f > > +2: > > +#endif > > LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e) > > LOAD_REG_IMMEDIATE(r15,interrupt_end_book3e) > > cmpld cr0,r10,r14 > > @@ -523,7 +550,7 @@ kernel_dbg_exc: > > blt+ cr0,1f > > bge+ cr1,1f > > > > - /* here it looks like we got an inappropriate debug exception. */ > > +3: /* here it looks like we got an inappropriate debug exception. */ > > lis r14,DBSR_IC@h /* clear the IC event */ > > rlwinm r11,r11,0,~MSR_DE /* clear DE in the DSRR1 value */ > > mtspr SPRN_DBSR,r14 > > diff --git a/arch/powerpc/kernel/head_booke.h > > b/arch/powerpc/kernel/head_booke.h > > index 5f051ee..edc6a3b 100644 > > --- a/arch/powerpc/kernel/head_booke.h > > +++ b/arch/powerpc/kernel/head_booke.h > > @@ -285,7 +285,33 @@ label: > > mfspr r10,SPRN_DBSR; /* check single-step/branch taken */ \ > > andis. r10,r10,(DBSR_IC|DBSR_BT)@h; \ > > beq+ 2f; \ > > +#ifdef CONFIG_KVM_BOOKE_HV \ > > + /* \ > > + * EPCR.DUVD controls whether the debug events can come in \ > > + * hypervisor mode or not. When KVM guest is using the debug \ > > + * resource then we do not want debug events to be captured \ > > + * in guest entry/exit path. So we set EPCR.DUVD when entering \ > > + * and clears EPCR.DUVD when exiting from guest. \ > > + * Debug instruction complete is a post-completion debug \ > > + * exception but debug event gets posted on the basis of MSR \ > > + * before the instruction is executed. Now if the instruction \ > > + * switches the context from guest mode (MSR.GS = 1) to hypervisor \ > > + * mode (MSR.GS = 0) then the xSRR0 points to first instruction of \ > > + * KVM handler and xSRR1 points that MSR.GS is clear \ > > + * (hypervisor context). Now as xSRR1.GS is used to decide whether \ > > + * KVM handler will be invoked to handle the exception or host \ > > + * host kernel debug handler will be invoked to handle the exception. \ > > + * This leads to host kernel debug handler handling the exception \ > > + * which should either be handled by KVM. \ > > + */ \ > > + mfspr r10, SPRN_EPCR; \ > > + andis. r10,r10,SPRN_EPCR_DUVD@h; \ > > + beq+ 3f; \ > > \ > > + andis. r10,r9,MSR_GS@h; \ > > + beq+ 1f; \ > > +3: \ > > +#endif \ > > lis r10,KERNELBASE@h; /* check if exception in vectors */ \ > > ori r10,r10,KERNELBASE@l; \ > > cmplw r12,r10; \ > > -- > > 1.7.0.4 > > > > > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in > > the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info > > at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
