Re: [PATCH v3 02/41] KVM: PPC: Book3S HV: Prevent radix guests from setting LPCR[TC]

Excerpts from Fabiano Rosas's message of March 9, 2021 1:47 am:

Nicholas Piggin [off-list ref] writes:

quoted

This bit only applies to hash partitions.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kvm/book3s_hv.c        | 6 ++++--
 arch/powerpc/kvm/book3s_hv_nested.c | 2 +-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index c40eeb20be39..2e29b96ef775 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c

@@ -1666,10 +1666,12 @@ static void kvmppc_set_lpcr(struct kvm_vcpu *vcpu, u64 new_lpcr,

 	/*
 	 * Userspace can only modify DPFD (default prefetch depth),
-	 * ILE (interrupt little-endian) and TC (translation control).
+	 * ILE (interrupt little-endian) and TC (translation control) if HPT.
 	 * On POWER8 and POWER9 userspace can also modify AIL (alt. interrupt loc.).
 	 */
-	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC;
+	mask = LPCR_DPFD | LPCR_ILE;
+	if (!kvm_is_radix(kvm))
+		mask |= LPCR_TC;

I think in theory there is a possibility that userspace sets the LPCR
while we running Radix and then calls the KVM_PPC_CONFIGURE_V3_MMU ioctl
right after to switch to HPT. I'm not sure if that would make sense but
maybe it's something to consider...

Oh actually it is an issue for the later AIL patch I think.

So LPCR will have to be filtered again when switching MMU mode.

Good catch, I'll add something for that.

Thanks,
Nick

quoted

 	if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
 		mask |= LPCR_AIL;
 		/* LPCR[AIL]=1/2 is disallowed */

diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index b496079e02f7..0e6cf650cbfe 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c

@@ -141,7 +141,7 @@ static void sanitise_hv_regs(struct kvm_vcpu *vcpu, struct hv_guest_state *hr)
 	 * Don't let L1 change LPCR bits for the L2 except these:
 	 * Keep this in sync with kvmppc_set_lpcr.
 	 */
-	mask = LPCR_DPFD | LPCR_ILE | LPCR_TC | LPCR_LD | LPCR_LPES | LPCR_MER;
+	mask = LPCR_DPFD | LPCR_ILE | LPCR_LD | LPCR_LPES | LPCR_MER;
 	/* LPCR[AIL]=1/2 is disallowed */
 	if ((hr->lpcr & LPCR_AIL) && (hr->lpcr & LPCR_AIL) != LPCR_AIL_3)
 		hr->lpcr &= ~LPCR_AIL;