Re: [PATCH 08/27] Add SLB switching code for entry/exit

Alexander Graf
2009-11-02T09:59:09Z

Am 02.11.2009 um 10:39 schrieb Michael Neuling <mikey@neuling.org>:

>>>> This is the really low level of guest entry/exit code.
>>>>
>>>> Book3s_64 has an SLB, which stores all ESID -> VSID mappings we're
>>>> currently aware of.
>>>>
>>>> The segments in the guest differ from the ones on the host, so we
>>>> need
>>>> to switch the SLB to tell the MMU that we're in a new context.
>>>>
>>>> So we store a shadow of the guest's SLB in the PACA, switch to that
>>>> on
>>>> entry and only restore bolted entries on exit, leaving the rest to
>>>> the
>>>> Linux SLB fault handler.
>>>>
>>>> That way we get a really clean way of switching the SLB.
>>>>
>>>> Signed-off-by: Alexander Graf <agraf@suse.de>
>>>> ---
>>>> arch/powerpc/kvm/book3s_64_slb.S | 277 ++++++++++++++++++++++++++
>>>> ++
>>>> ++++++++
>>> ++
>>>> 1 files changed, 277 insertions(+), 0 deletions(-)
>>>> create mode 100644 arch/powerpc/kvm/book3s_64_slb.S
>>>>
>>>> diff --git a/arch/powerpc/kvm/book3s_64_slb.S b/arch/powerpc/kvm/
>>>> book3s_64_sl
>>> b.S
>>>> new file mode 100644
>>>> index 0000000..00a8367
>>>> --- /dev/null
>>>> +++ b/arch/powerpc/kvm/book3s_64_slb.S
>>>> @@ -0,0 +1,277 @@
>>>> +/*
>>>> + * This program is free software; you can redistribute it and/or
>>>> modify
>>>> + * it under the terms of the GNU General Public License, version
>>>> 2, as
>>>> + * published by the Free Software Foundation.
>>>> + *
>>>> + * This program is distributed in the hope that it will be useful,
>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
>>>> + * GNU General Public License for more details.
>>>> + *
>>>> + * You should have received a copy of the GNU General Public
>>>> License
>>>> + * along with this program; if not, write to the Free Software
>>>> + * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
>>>> 02110-1301, USA.
>>>> + *
>>>> + * Copyright SUSE Linux Products GmbH 2009
>>>> + *
>>>> + * Authors: Alexander Graf <agraf@suse.de>
>>>> + */
>>>> +
>>>> +/
>>>> ***
>>>> ***
>>>> ***
>>>> ******************************************************************
>>> ***
>>>> + *
>>> *
>>>> + * Entry code
>>> *
>>>> + *
>>> *
>>>> +
>>>> ***
>>>> ***
>>>> ***
>>>> ******************************************************************
>>> **/
>>>> +
>>>> +.global kvmppc_handler_trampoline_enter
>>>> +kvmppc_handler_trampoline_enter:
>>>> +
>>>> + /* Required state:
>>>> + *
>>>> + * MSR = ~IR|DR
>>>> + * R13 = PACA
>>>> + * R9 = guest IP
>>>> + * R10 = guest MSR
>>>> + * R11 = free
>>>> + * R12 = free
>>>> + * PACA[PACA_EXMC + EX_R9] = guest R9
>>>> + * PACA[PACA_EXMC + EX_R10] = guest R10
>>>> + * PACA[PACA_EXMC + EX_R11] = guest R11
>>>> + * PACA[PACA_EXMC + EX_R12] = guest R12
>>>> + * PACA[PACA_EXMC + EX_R13] = guest R13
>>>> + * PACA[PACA_EXMC + EX_CCR] = guest CR
>>>> + * PACA[PACA_EXMC + EX_R3] = guest XER
>>>> + */
>>>> +
>>>> + mtsrr0 r9
>>>> + mtsrr1 r10
>>>> +
>>>> + mtspr SPRN_SPRG_SCRATCH0, r0
>>>> +
>>>> + /* Remove LPAR shadow entries */
>>>> +
>>>> +#if SLB_NUM_BOLTED == 3
>>>
>>> You could alternatively check the persistent entry in the
>>> slb_shawdow
>>> buffer. This would give you a run time check. Not sure what's best
>>> though.
>>
>> Well we're in the hot path here, so anything using as few registers
>> as
>> possible and being simple is the best :-). I'd guess the more we are
>> clever at compile time the better.
>
> Yeah, I tend to agree.
>
>>
>>>
>>>
>>>> +
>>>> + ld r12, PACA_SLBSHADOWPTR(r13)
>>>> + ld r10, 0x10(r12)
>>>> + ld r11, 0x18(r12)
>>>
>>> Can you define something in asm-offsets.c for these magic constants
>>> 0x10
>>> and 0x18. Similarly below.
>>>
>>>> + /* Invalid? Skip. */
>>>> + rldicl. r0, r10, 37, 63
>>>> + beq slb_entry_skip_1
>>>> + xoris r9, r10, SLB_ESID_V@h
>>>> + std r9, 0x10(r12)
>>>> +slb_entry_skip_1:
>>>> + ld r9, 0x20(r12)
>>>> + /* Invalid? Skip. */
>>>> + rldicl. r0, r9, 37, 63
>>>> + beq slb_entry_skip_2
>>>> + xoris r9, r9, SLB_ESID_V@h
>>>> + std r9, 0x20(r12)
>>>> +slb_entry_skip_2:
>>>> + ld r9, 0x30(r12)
>>>> + /* Invalid? Skip. */
>>>> + rldicl. r0, r9, 37, 63
>>>> + beq slb_entry_skip_3
>>>> + xoris r9, r9, SLB_ESID_V@h
>>>> + std r9, 0x30(r12)
>>>
>>> Can these 3 be made into a macro?
>>
>> Phew - dynamically generating jump points sounds rather hard. I can
>> give it a try...
>>
>>>
>>>> +slb_entry_skip_3:
>>>> +
>>>> +#else
>>>> +#error unknown number of bolted entries
>>>> +#endif
>>>> +
>>>> + /* Flush SLB */
>>>> +
>>>> + slbia
>>>> +
>>>> + /* r0 = esid & ESID_MASK */
>>>> + rldicr r10, r10, 0, 35
>>>> + /* r0 |= CLASS_BIT(VSID) */
>>>> + rldic r12, r11, 56 - 36, 36
>>>> + or r10, r10, r12
>>>> + slbie r10
>>>> +
>>>> + isync
>>>> +
>>>> + /* Fill SLB with our shadow */
>>>> +
>>>> + lbz r12, PACA_KVM_SLB_MAX(r13)
>>>> + mulli r12, r12, 16
>>>> + addi r12, r12, PACA_KVM_SLB
>>>> + add r12, r12, r13
>>>> +
>>>> + /* for (r11 = kvm_slb; r11 < kvm_slb + kvm_slb_size;
>>>> r11+=slb_entry) */
>>>> + li r11, PACA_KVM_SLB
>>>> + add r11, r11, r13
>>>> +
>>>> +slb_loop_enter:
>>>> +
>>>> + ld r10, 0(r11)
>>>> +
>>>> + rldicl. r0, r10, 37, 63
>>>> + beq slb_loop_enter_skip
>>>> +
>>>> + ld r9, 8(r11)
>>>> + slbmte r9, r10
>>>
>>> If you're updating the first 3 slbs, you need to make sure the slb
>>> shadow is updated at the same time
>>
>> Well - what happens if we don't? We'd get a segment fault when phyp
>> stole our entry! So what? Let it fault, see the mapping is already
>> there and get back in again :-).
>
> The problem is you won't take the segment fault as PHYP may put a
> valid
> entry in there. PHYP will put back what's in the shadow buffer, which
> could be valid hence no segment fault.

The shadow buffer contains V=0 entries :).

Alex

>
>>> (BTW dumb question: can we run this
>>> under PHYP?)
>>
>> Yes, I tested it on bare metal, phyp and a PS3.
>
> Nice!
>
> Mikey
> --
> To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html