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

On 07/04/2012 01:15 PM, Caraman Mihai Claudiu-B02008 wrote:

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________________________________________
From: Alexander Graf [agraf@suse.de]
Sent: Wednesday, July 04, 2012 6:45 PM
To: Caraman Mihai Claudiu-B02008
Cc: <redacted>; KVM list; linuxppc-dev; qemu-ppc@nongnu.org List; Benjamin Herrenschmidt
Subject: Re: [Qemu-ppc] [RFC PATCH 12/17] PowerPC: booke64: Add DO_KVM kernel hooks

On 04.07.2012, at 17:27, Caraman Mihai Claudiu-B02008 wrote:

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-----Original Message-----
From: Alexander Graf [mailto:agraf@suse.de]
Sent: Wednesday, July 04, 2012 5:30 PM
To: Caraman Mihai Claudiu-B02008
Cc: <redacted>; KVM list; linuxppc-dev; qemu-
ppc@nongnu.org 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:

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Hook DO_KVM macro to 64-bit booke in a optimal way similar to 32-bit

booke

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see head_fsl_booke.S file. Extend interrupt handlers' parameter list

with

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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 <redacted>
---
arch/powerpc/kernel/exceptions-64e.S |  114 ++++++++++++++++++++++++---

-------

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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

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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.

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

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

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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.

I don't get the point then. Why not have the whole DO_KVM masked under FTR_SECTION_IFSET(CPU_FTR_EMB_HV)? Are there book3s_64 implementations without HV? 

I guess you refer to book3e_64. I don't know all implementations but Embedded.HV category is optional.

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Can't we just mfspr unconditionally in DO_KVM?

I think Scott should better answer this question, I don't know why he opted for the other approach.

That was on 32-bit, where some of DO_KVM's users want SRR1 for their own
purposes.

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-.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 ;)

You could #ifdef it in DO_KVM for 64-bit for now. IIRC it's not done on 32-bit because the register value is used even beyond DO_KVM there.

Nope, 32-bit code is also guarded by CONFIG_KVM_BOOKE_HV.

Only in the TLB miss handlers, not the normal exception prolog.

-Scott