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KVM: PPC: Book3S HV: Work around XER[SO] bug in fake suspend mode

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This works around a hardware bug in "Nimbus" POWER9 DD2.2 processors,
where a treclaim performed in fake suspend mode can cause subsequent
reads from the XER register to return inconsistent values for the SO
(summary overflow) bit.  The inconsistent SO bit state can potentially
be observed on any thread in the core.  We have to do the treclaim
because that is the only way to get the thread out of suspend state
(fake or real) and into non-transactional state.

The workaround for the bug is to force the core into SMT4 mode before
doing the treclaim.  This patch adds the code to do that, conditional
on the CPU_FTR_P9_TM_XER_SO_BUG feature bit.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Suraj Jitindar Singh 2018-03-21 21:32:02 +11:00 committed by Michael Ellerman
parent 4bb3c7a020
commit 87a11bb6a7
1 changed files with 20 additions and 4 deletions
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24
arch/powerpc/kvm/book3s_hv_rmhandlers.S
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@ -3101,6 +3101,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
kvmppc_save_tm:
mflr r0
std r0, PPC_LR_STKOFF(r1)
stdu r1, -PPC_MIN_STKFRM(r1)
/* Turn on TM. */
mfmsr r8
@ -3120,8 +3121,16 @@ BEGIN_FTR_SECTION
mfspr r6, SPRN_TEXASR
std r6, VCPU_ORIG_TEXASR(r9)
rldicl. r8, r8, 64 - MSR_TS_S_LG, 62
lbz r0, HSTATE_FAKE_SUSPEND(r13) /* Were we fake suspended? */
cmpwi r0, 0
beq 3f
rldicl. r8, r8, 64 - MSR_TS_S_LG, 62 /* Did we actually hrfid? */
beq 4f
BEGIN_FTR_SECTION_NESTED(96)
bl pnv_power9_force_smt4_catch
END_FTR_SECTION_NESTED(CPU_FTR_P9_TM_XER_SO_BUG, CPU_FTR_P9_TM_XER_SO_BUG, 96)
nop
3:
END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
/* Clear the MSR RI since r1, r13 are all going to be foobar. */
@ -3138,7 +3147,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
/* If doing TM emulation on POWER9 DD2.2, check for fake suspend mode */
BEGIN_FTR_SECTION
3:
lbz r9, HSTATE_FAKE_SUSPEND(r13)
cmpwi r9, 0
beq 2f
@ -3150,13 +3158,18 @@ BEGIN_FTR_SECTION
/* Reload stack pointer and TOC. */
ld r1, HSTATE_HOST_R1(r13)
ld r2, PACATOC(r13)
/* Set MSR RI now we have r1 and r13 back. */
li r5, MSR_RI
mtmsrd r5, 1
HMT_MEDIUM
ld r6, HSTATE_DSCR(r13)
mtspr SPRN_DSCR, r6
li r0, 0
stb r0, HSTATE_FAKE_SUSPEND(r13)
BEGIN_FTR_SECTION_NESTED(96)
bl pnv_power9_force_smt4_release
END_FTR_SECTION_NESTED(CPU_FTR_P9_TM_XER_SO_BUG, CPU_FTR_P9_TM_XER_SO_BUG, 96)
nop
4:
mfspr r3, SPRN_PSSCR
/* PSSCR_FAKE_SUSPEND is a write-only bit, but clear it anyway */
li r0, PSSCR_FAKE_SUSPEND
@ -3244,6 +3257,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_P9_TM_HV_ASSIST)
std r6, VCPU_TFIAR(r9)
std r7, VCPU_TEXASR(r9)
addi r1, r1, PPC_MIN_STKFRM
ld r0, PPC_LR_STKOFF(r1)
mtlr r0
blr
@ -3278,6 +3292,8 @@ kvmppc_restore_tm:
mtspr SPRN_TFIAR, r6
mtspr SPRN_TEXASR, r7
li r0, 0
stb r0, HSTATE_FAKE_SUSPEND(r13)
ld r5, VCPU_MSR(r4)
rldicl. r5, r5, 64 - MSR_TS_S_LG, 62
beqlr /* TM not active in guest */