PR KVM does not support running with AIL enabled, and SCV does is not
supported with AIL disabled.
Fix this by ensuring the SCV facility is disabled with FSCR while a
CPU can be running with AIL=0. PowerNV host supports disabling AIL on a
per-CPU basis, so SCV just needs to be disabled when a vCPU is run.
The pSeries machine can only switch AIL on a system-wide basis, so it
must disable SCV support at boot if the configuration can potentially
run a PR KVM guest.
Alternatives considered and rejected:
- SCV support can not be disabled by PR KVM after boot, because it is
advertised to userspace with HWCAP.
- AIL can not be disabled on a per-CPU basis. At least when running on
pseries it is a per-LPAR setting.
- Support for real-mode SCV vectors will not be added because they are
at 0x17000 so making such a large fixed head space causes immediate
value limits to be exceeded, requiring a lot rework and more code.
- Disabling SCV for any PR KVM possible kernel will cause a slowdown
when not using PR KVM.
- A boot time option to disable SCV to use PR KVM is user-hostile.
- System call instruction emulation for SCV facility unavailable
instructions is too complex and old emulation code was subtly broken
and removed.
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
arch/powerpc/kernel/exceptions-64s.S | 4 ++++
arch/powerpc/kernel/setup_64.c | 15 +++++++++++++++
arch/powerpc/kvm/book3s_pr.c | 20 ++++++++++++++------
3 files changed, 33 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/kernel/exceptions-64s.S
b/arch/powerpc/kernel/exceptions-64s.S
index 55caeee37c08..b66dd6f775a4 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -809,6 +809,10 @@ __start_interrupts:
* - MSR_EE|MSR_RI is clear (no reentrant exceptions)
* - Standard kernel environment is set up (stack, paca, etc)
*
+ * KVM:
+ * These interrupts do not elevate HV 0->1, so HV is not involved. PR KVM
+ * ensures that FSCR[SCV] is disabled whenever it has to force AIL off.
+ *
* Call convention:
*
* syscall register convention is in Documentation/powerpc/syscall64-abi.rst
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index d87f7c1103ce..5b8740ece1b2 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -197,6 +197,21 @@ static void __init configure_exceptions(void)
/* Under a PAPR hypervisor, we need hypercalls */
if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
+ /*
+ * PR KVM does not support AIL mode interrupts in the host, and
+ * SCV system call interrupt vectors are only implemented for
+ * AIL mode. Under pseries, AIL mode can only be enabled and
+ * disabled system-wide so when PR KVM is loaded, all CPUs in
+ * the host are set to AIL=0 mode. SCV can not be disabled
+ * dynamically because the feature is advertised to host
+ * userspace, so SCV support must not be enabled if PR KVM can
+ * possibly be run.
+ */
+ if (IS_ENABLED(CONFIG_KVM_BOOK3S_PR_POSSIBLE) &&
!radix_enabled()) {
+ init_task.thread.fscr &= ~FSCR_SCV;
+ cur_cpu_spec->cpu_user_features2 &= ~PPC_FEATURE2_SCV;
+ }
+
/* Enable AIL if possible */
if (!pseries_enable_reloc_on_exc()) {
init_task.thread.fscr &= ~FSCR_SCV;
diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 6bc9425acb32..9845bd509185 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -140,9 +140,12 @@ static void kvmppc_core_vcpu_load_pr(struct kvm_vcpu
*vcpu, int cpu)
#endif
/* Disable AIL if supported */
- if (cpu_has_feature(CPU_FTR_HVMODE) &&
- cpu_has_feature(CPU_FTR_ARCH_207S))
- mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) & ~LPCR_AIL);
+ if (cpu_has_feature(CPU_FTR_HVMODE)) {
+ if (cpu_has_feature(CPU_FTR_ARCH_207S))
+ mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) & ~LPCR_AIL);
+ if (cpu_has_feature(CPU_FTR_ARCH_300) && (current->thread.fscr
& FSCR_SCV))
+ mtspr(SPRN_FSCR, mfspr(SPRN_FSCR) & ~FSCR_SCV);
+ }
vcpu->cpu = smp_processor_id();
#ifdef CONFIG_PPC_BOOK3S_32
@@ -175,9 +178,12 @@ static void kvmppc_core_vcpu_put_pr(struct kvm_vcpu *vcpu)
kvmppc_save_tm_pr(vcpu);
/* Enable AIL if supported */
- if (cpu_has_feature(CPU_FTR_HVMODE) &&
- cpu_has_feature(CPU_FTR_ARCH_207S))
- mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) | LPCR_AIL_3);
+ if (cpu_has_feature(CPU_FTR_HVMODE)) {
+ if (cpu_has_feature(CPU_FTR_ARCH_207S))
+ mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) | LPCR_AIL_3);
+ if (cpu_has_feature(CPU_FTR_ARCH_300) && (current->thread.fscr
& FSCR_SCV))
+ mtspr(SPRN_FSCR, mfspr(SPRN_FSCR) | FSCR_SCV);
+ }
vcpu->cpu = -1;
}
@@ -1037,6 +1043,8 @@ static int kvmppc_handle_fac(struct kvm_vcpu *vcpu, ulong
fac)
void kvmppc_set_fscr(struct kvm_vcpu *vcpu, u64 fscr)
{
+ if (fscr & FSCR_SCV)
+ fscr &= ~FSCR_SCV; /* SCV must not be enabled */
if ((vcpu->arch.fscr & FSCR_TAR) && !(fscr & FSCR_TAR)) {
/* TAR got dropped, drop it in shadow too */
kvmppc_giveup_fac(vcpu, FSCR_TAR_LG);
--
2.23.0
