From 267cdfa21385d78c794768233678756e32b39ead Mon Sep 17 00:00:00 2001
From: Nicholas Piggin <npiggin@gmail.com>
Date: Wed, 8 Sep 2021 20:17:18 +1000
Subject: [PATCH] KVM: PPC: Book3S HV: Tolerate treclaim. in fake-suspend mode
changing registers
References: bsc#1156395
Patch-mainline: v5.15-rc2
Git-commit: 267cdfa21385d78c794768233678756e32b39ead
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: 7854f7545bff ("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
Acked-by: Michal Suchanek <msuchanek@suse.de>
---
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 36 +++++++++++++++++++++++--
1 file changed, 34 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 75079397c2a5..90484425a1e6 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -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
--
2.31.1