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

commit 267cdfa21385d78c794768233678756e32b39ead upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index cd9995e..5777b72 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -3146,7 +3146,7 @@ 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
@@ -3161,10 +3161,42 @@ 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
@@ -3192,7 +3224,7 @@ 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