Re: [Qemu-ppc] [RFC PATCH 12/17] PowerPC: booke64: Add DO_KVM kernel hooks

[Caraman Mihai Claudiu-B02008]

> -----Original Message-----
> From: Alexander Graf [mailto:address@hidden
> Sent: Wednesday, July 04, 2012 5:30 PM
> To: Caraman Mihai Claudiu-B02008
> Cc: <address@hidden>; KVM list; linuxppc-dev; qemu-
> address@hidden List; Benjamin Herrenschmidt
> Subject: Re: [Qemu-ppc] [RFC PATCH 12/17] PowerPC: booke64: Add DO_KVM
> kernel hooks
> 
> 
> On 25.06.2012, at 14:26, Mihai Caraman wrote:
> 
> > Hook DO_KVM macro to 64-bit booke in a optimal way similar to 32-bit
> booke
> > see head_fsl_booke.S file. Extend interrupt handlers' parameter list
> with
> > interrupt vector numbers to accomodate the macro. Rework Guest Doorbell
> > handler to use the proper GSRRx save/restore registers.
> > Only the bolted version of tlb miss handers is addressed now.
> >
> > Signed-off-by: Mihai Caraman <address@hidden>
> > ---
> > arch/powerpc/kernel/exceptions-64e.S |  114 ++++++++++++++++++++++++---
> -------
> > arch/powerpc/mm/tlb_low_64e.S        |   14 +++-
> > 2 files changed, 92 insertions(+), 36 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/exceptions-64e.S
> b/arch/powerpc/kernel/exceptions-64e.S
> > index 06f7aec..a60f81f 100644
> > --- a/arch/powerpc/kernel/exceptions-64e.S
> > +++ b/arch/powerpc/kernel/exceptions-64e.S
> > @@ -25,6 +25,8 @@
> > #include <asm/ppc-opcode.h>
> > #include <asm/mmu.h>
> > #include <asm/hw_irq.h>
> > +#include <asm/kvm_asm.h>
> > +#include <asm/kvm_booke_hv_asm.h>
> >
> > /* XXX This will ultimately add space for a special exception save
> >  *     structure used to save things like SRR0/SRR1, SPRGs, MAS, etc...
> > @@ -34,13 +36,24 @@
> >  */
> > #define     SPECIAL_EXC_FRAME_SIZE  INT_FRAME_SIZE
> >
> > +#ifdef CONFIG_KVM_BOOKE_HV
> > +#define KVM_BOOKE_HV_MFSPR(reg, spr)                               \
> > +   BEGIN_FTR_SECTION                                       \
> > +           mfspr   reg, spr;                               \
> > +   END_FTR_SECTION_IFSET(CPU_FTR_EMB_HV)
> > +#else
> > +#define KVM_BOOKE_HV_MFSPR(reg, spr)
> > +#endif
> 
> Bleks - this is ugly.

I agree :) But I opted to keep the optimizations done for 32-bit.

> Do we really need to open-code the #ifdef here?

32-bit implementation fortunately use asm macros, we can't nest defines.

> Can't the feature section code determine that the feature is disabled and
> just always not include the code?

CPU_FTR_EMB_HV is set even if KVM is not configured.

> 
> > +
> > /* Exception prolog code for all exceptions */
> > -#define EXCEPTION_PROLOG(n, type, srr0, srr1, addition)
> \
> > +#define EXCEPTION_PROLOG(n, intnum, type, srr0, srr1, addition)
>           \
> >     mtspr   SPRN_SPRG_##type##_SCRATCH,r13; /* get spare registers */
> \
> >     mfspr   r13,SPRN_SPRG_PACA;     /* get PACA */                      \
> >     std     r10,PACA_EX##type+EX_R10(r13);                              \
> >     std     r11,PACA_EX##type+EX_R11(r13);                              \
> >     mfcr    r10;                    /* save CR */                       \
> > +   KVM_BOOKE_HV_MFSPR(r11,srr1);                                       \
> > +   DO_KVM  intnum,srr1;                                                \
> 
> So if DO_KVM already knows srr1, why explicitly do something with it the
> line above, and not in DO_KVM itself?

srr1 is used to expand the interrupt handler symbol name while r11 is used
for the actual MSR[GS] optimal check:
        mtocrf  0x80, r11

> > -/* Guest Doorbell */
> > -   MASKABLE_EXCEPTION(0x2c0, guest_doorbell, .unknown_exception,
> ACK_NONE)
> > +/*
> > + * Guest doorbell interrupt
> > + * This general exception use GSRRx save/restore registers
> > + */
> > +   START_EXCEPTION(guest_doorbell);
> > +   EXCEPTION_PROLOG(0x2c0, BOOKE_INTERRUPT_GUEST_DBELL, GEN,
> > +                    SPRN_GSRR0, SPRN_GSRR1, PROLOG_ADDITION_NONE)
> > +   EXCEPTION_COMMON(0x2c0, PACA_EXGEN, INTS_KEEP)
> > +   addi    r3,r1,STACK_FRAME_OVERHEAD
> > +   bl      .save_nvgprs
> > +   INTS_RESTORE_HARD
> > +   bl      .unknown_exception
> > +   b       .ret_from_except
> 
> This is independent of DO_KVM, right?

Yes, just kvm_handler definitions in bookehv_interrupts.S depends on this.

> 
> >
> > /* Guest Doorbell critical Interrupt */
> >     START_EXCEPTION(guest_doorbell_crit);
> > -   CRIT_EXCEPTION_PROLOG(0x2e0, PROLOG_ADDITION_NONE)
> > +   CRIT_EXCEPTION_PROLOG(0x2e0, BOOKE_INTERRUPT_GUEST_DBELL_CRIT,
> > +                         PROLOG_ADDITION_NONE)
> 
> Shouldn't this one also use GSRR?

No, this is a critical exception.

> >
> > -.macro tlb_prolog_bolted addr
> > +.macro tlb_prolog_bolted intnum addr
> >     mtspr   SPRN_SPRG_TLB_SCRATCH,r13
> >     mfspr   r13,SPRN_SPRG_PACA
> >     std     r10,PACA_EXTLB+EX_TLB_R10(r13)
> >     mfcr    r10
> >     std     r11,PACA_EXTLB+EX_TLB_R11(r13)
> > +#ifdef CONFIG_KVM_BOOKE_HV
> > +BEGIN_FTR_SECTION
> > +   mfspr   r11, SPRN_SRR1
> > +END_FTR_SECTION_IFSET(CPU_FTR_EMB_HV)
> > +#endif
> 
> This thing really should vanish behind DO_KVM :)

Then let's do it first for 32-bit ;)

-Mike