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KVM: PPC: Book3S HV: Tolerate treclaim. in fake-suspend mode changing registers 

POWER9 DD2.2 and 2.3 hardware implements a "fake-suspend" mode where
certain TM instructions executed in HV=0 mode cause softpatch interrupts
so the hypervisor can emulate them and prevent problematic processor
conditions. In this fake-suspend mode, the treclaim. instruction does
not modify registers.

Unfortunately the rfscv instruction executed by the guest do not
generate softpatch interrupts, which can cause the hypervisor to lose
track of the fake-suspend mode, and it can execute this treclaim. while
not in fake-suspend mode. This modifies GPRs and crashes the hypervisor.

It's not trivial to disable scv in the guest with HFSCR now, because
they assume a POWER9 has scv available. So this fix saves and restores
checkpointed registers across the treclaim.

Fixes: 7854f7545b ("KVM: PPC: Book3S: Rework TM save/restore code and make it C-callable")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210908101718.118522-2-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2021-09-08 20:17:18 +10:00 committed by Michael Ellerman
parent ae7aaecc3f
commit 267cdfa213
1 changed files with 34 additions and 2 deletions
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36
arch/powerpc/kvm/book3s_hv_rmhandlers.S
View File

@ -2536,7 +2536,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_P9_TM_HV_ASSIST)
/* The following code handles the fake_suspend = 1 case */
mflr r0
std r0, PPC_LR_STKOFF(r1)
stdu r1, -PPC_MIN_STKFRM(r1)
stdu r1, -TM_FRAME_SIZE(r1)
/* Turn on TM. */
mfmsr r8
@ -2551,10 +2551,42 @@ BEGIN_FTR_SECTION
END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_XER_SO_BUG)
nop
/*
* It's possible that treclaim. may modify registers, if we have lost
* track of fake-suspend state in the guest due to it using rfscv.
* Save and restore registers in case this occurs.
*/
mfspr r3, SPRN_DSCR
mfspr r4, SPRN_XER
mfspr r5, SPRN_AMR
/* SPRN_TAR would need to be saved here if the kernel ever used it */
mfcr r12
SAVE_NVGPRS(r1)
SAVE_GPR(2, r1)
SAVE_GPR(3, r1)
SAVE_GPR(4, r1)
SAVE_GPR(5, r1)
stw r12, 8(r1)
std r1, HSTATE_HOST_R1(r13)
/* We have to treclaim here because that's the only way to do S->N */
li r3, TM_CAUSE_KVM_RESCHED
TRECLAIM(R3)
GET_PACA(r13)
ld r1, HSTATE_HOST_R1(r13)
REST_GPR(2, r1)
REST_GPR(3, r1)
REST_GPR(4, r1)
REST_GPR(5, r1)
lwz r12, 8(r1)
REST_NVGPRS(r1)
mtspr SPRN_DSCR, r3
mtspr SPRN_XER, r4
mtspr SPRN_AMR, r5
mtcr r12
HMT_MEDIUM
/*
* We were in fake suspend, so we are not going to save the
* register state as the guest checkpointed state (since
@ -2582,7 +2614,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_XER_SO_BUG)
std r5, VCPU_TFHAR(r9)
std r6, VCPU_TFIAR(r9)
addi r1, r1, PPC_MIN_STKFRM
addi r1, r1, TM_FRAME_SIZE
ld r0, PPC_LR_STKOFF(r1)
mtlr r0
blr