[PATCH v2 30/37] KVM: PPC: Book3S HV: Implement radix prefetch workaround by disabling MMU
Nicholas Piggin
npiggin at gmail.com
Fri Feb 26 00:46:45 AEDT 2021
Rather than partition the guest PID space and catch and flush a rogue
guest, instead work around this issue by ensuring the MMU is always
disabled in HV mode while the guest MMU context is switched in.
This may be a bit less efficient, but it is a lot less complicated and
allows the P9 path to trivally implement the workaround too. Newer CPUs
are not subject to this issue.
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
arch/powerpc/include/asm/mmu_context.h | 6 ----
arch/powerpc/kvm/book3s_hv.c | 10 ++++--
arch/powerpc/kvm/book3s_hv_interrupt.c | 14 ++++++--
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 34 ------------------
arch/powerpc/mm/book3s64/radix_pgtable.c | 27 +++++---------
arch/powerpc/mm/book3s64/radix_tlb.c | 46 ------------------------
arch/powerpc/mm/mmu_context.c | 4 +--
7 files changed, 28 insertions(+), 113 deletions(-)
diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 652ce85f9410..bb5c7e5e142e 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h
@@ -122,12 +122,6 @@ static inline bool need_extra_context(struct mm_struct *mm, unsigned long ea)
}
#endif
-#if defined(CONFIG_KVM_BOOK3S_HV_POSSIBLE) && defined(CONFIG_PPC_RADIX_MMU)
-extern void radix_kvm_prefetch_workaround(struct mm_struct *mm);
-#else
-static inline void radix_kvm_prefetch_workaround(struct mm_struct *mm) { }
-#endif
-
extern void switch_cop(struct mm_struct *next);
extern int use_cop(unsigned long acop, struct mm_struct *mm);
extern void drop_cop(unsigned long acop, struct mm_struct *mm);
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index ad16331c3370..c3064075f1d7 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -806,6 +806,10 @@ static int kvmppc_h_set_mode(struct kvm_vcpu *vcpu, unsigned long mflags,
/* KVM does not support mflags=2 (AIL=2) */
if (mflags != 0 && mflags != 3)
return H_UNSUPPORTED_FLAG_START;
+ /* Prefetch bug */
+ if (cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG) &&
+ kvmhv_vcpu_is_radix(vcpu) && mflags == 3)
+ return H_UNSUPPORTED_FLAG_START;
return H_TOO_HARD;
default:
return H_TOO_HARD;
@@ -4286,8 +4290,7 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
* The TLB prefetch bug fixup is only in the kvmppc_run_vcpu
* path, which also handles hash and dependent threads mode.
*/
- if (kvm->arch.threads_indep && kvm_is_radix(kvm) &&
- !cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
+ if (kvm->arch.threads_indep && kvm_is_radix(kvm))
r = kvmhv_run_single_vcpu(vcpu, ~(u64)0,
vcpu->arch.vcore->lpcr);
else
@@ -4914,6 +4917,9 @@ static int kvmppc_core_init_vm_hv(struct kvm *kvm)
if (!indep_threads_mode && !cpu_has_feature(CPU_FTR_HVMODE)) {
pr_warn("KVM: Ignoring indep_threads_mode=N in nested hypervisor\n");
kvm->arch.threads_indep = true;
+ } else if (!indep_threads_mode && cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) {
+ pr_warn("KVM: Ignoring indep_threads_mode=N on pre-DD2.2 POWER9\n");
+ kvm->arch.threads_indep = true;
} else {
kvm->arch.threads_indep = indep_threads_mode;
}
diff --git a/arch/powerpc/kvm/book3s_hv_interrupt.c b/arch/powerpc/kvm/book3s_hv_interrupt.c
index b93d861d8538..9784da3f8565 100644
--- a/arch/powerpc/kvm/book3s_hv_interrupt.c
+++ b/arch/powerpc/kvm/book3s_hv_interrupt.c
@@ -223,6 +223,9 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
mtspr(SPRN_AMOR, ~0UL);
+ if (cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
+ __mtmsrd(msr & ~(MSR_IR|MSR_DR|MSR_RI), 0);
+
switch_mmu_to_guest_radix(kvm, vcpu, lpcr);
/*
@@ -231,7 +234,8 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
*/
mtspr(SPRN_HDEC, hdec);
- __mtmsrd(0, 1); /* clear RI */
+ if (!cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
+ __mtmsrd(0, 1); /* clear RI */
mtspr(SPRN_DAR, vcpu->arch.shregs.dar);
mtspr(SPRN_DSISR, vcpu->arch.shregs.dsisr);
@@ -338,8 +342,6 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
radix_clear_slb();
- __mtmsrd(msr, 0);
-
accumulate_time(vcpu, &vcpu->arch.rm_exit);
/* Advance host PURR/SPURR by the amount used by guest */
@@ -406,6 +408,12 @@ int kvmhv_vcpu_entry_p9(struct kvm_vcpu *vcpu, u64 time_limit, unsigned long lpc
switch_mmu_to_host_radix(kvm, host_pidr);
+ /*
+ * If we are in real mode, don't switch MMU on until the MMU is
+ * switched to host, to avoid the P9 radix prefetch bug.
+ */
+ __mtmsrd(msr, 0);
+
end_timing(vcpu);
return trap;
diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 6118e8a97ddd..61f71a7df238 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -1710,40 +1710,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
eieio
tlbsync
ptesync
-
-BEGIN_FTR_SECTION
- /* Radix: Handle the case where the guest used an illegal PID */
- LOAD_REG_ADDR(r4, mmu_base_pid)
- lwz r3, VCPU_GUEST_PID(r9)
- lwz r5, 0(r4)
- cmpw cr0,r3,r5
- blt 2f
-
- /*
- * Illegal PID, the HW might have prefetched and cached in the TLB
- * some translations for the LPID 0 / guest PID combination which
- * Linux doesn't know about, so we need to flush that PID out of
- * the TLB. First we need to set LPIDR to 0 so tlbiel applies to
- * the right context.
- */
- li r0,0
- mtspr SPRN_LPID,r0
- isync
-
- /* Then do a congruence class local flush */
- ld r6,VCPU_KVM(r9)
- lwz r0,KVM_TLB_SETS(r6)
- mtctr r0
- li r7,0x400 /* IS field = 0b01 */
- ptesync
- sldi r0,r3,32 /* RS has PID */
-1: PPC_TLBIEL(7,0,2,1,1) /* RIC=2, PRS=1, R=1 */
- addi r7,r7,0x1000
- bdnz 1b
- ptesync
-END_FTR_SECTION_IFSET(CPU_FTR_P9_RADIX_PREFETCH_BUG)
-
-2:
#endif /* CONFIG_PPC_RADIX_MMU */
/*
diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index 98f0b243c1ab..1ea95891a79e 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -357,30 +357,19 @@ static void __init radix_init_pgtable(void)
}
/* Find out how many PID bits are supported */
- if (!cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) {
- if (!mmu_pid_bits)
- mmu_pid_bits = 20;
- mmu_base_pid = 1;
- } else if (cpu_has_feature(CPU_FTR_HVMODE)) {
- if (!mmu_pid_bits)
- mmu_pid_bits = 20;
-#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+ if (!cpu_has_feature(CPU_FTR_HVMODE) &&
+ cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG)) {
/*
- * When KVM is possible, we only use the top half of the
- * PID space to avoid collisions between host and guest PIDs
- * which can cause problems due to prefetch when exiting the
- * guest with AIL=3
+ * Older versions of KVM on these machines perfer if the
+ * guest only uses the low 19 PID bits.
*/
- mmu_base_pid = 1 << (mmu_pid_bits - 1);
-#else
- mmu_base_pid = 1;
-#endif
- } else {
- /* The guest uses the bottom half of the PID space */
if (!mmu_pid_bits)
mmu_pid_bits = 19;
- mmu_base_pid = 1;
+ } else {
+ if (!mmu_pid_bits)
+ mmu_pid_bits = 20;
}
+ mmu_base_pid = 1;
/*
* Allocate Partition table and process table for the
diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
index 409e61210789..312236a6b085 100644
--- a/arch/powerpc/mm/book3s64/radix_tlb.c
+++ b/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -1336,49 +1336,3 @@ void radix__flush_tlb_all(void)
: : "r"(rb), "i"(r), "i"(prs), "i"(ric), "r"(0) : "memory");
asm volatile("eieio; tlbsync; ptesync": : :"memory");
}
-
-#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
-extern void radix_kvm_prefetch_workaround(struct mm_struct *mm)
-{
- unsigned long pid = mm->context.id;
-
- if (unlikely(pid == MMU_NO_CONTEXT))
- return;
-
- if (!cpu_has_feature(CPU_FTR_P9_RADIX_PREFETCH_BUG))
- return;
-
- /*
- * If this context hasn't run on that CPU before and KVM is
- * around, there's a slim chance that the guest on another
- * CPU just brought in obsolete translation into the TLB of
- * this CPU due to a bad prefetch using the guest PID on
- * the way into the hypervisor.
- *
- * We work around this here. If KVM is possible, we check if
- * any sibling thread is in KVM. If it is, the window may exist
- * and thus we flush that PID from the core.
- *
- * A potential future improvement would be to mark which PIDs
- * have never been used on the system and avoid it if the PID
- * is new and the process has no other cpumask bit set.
- */
- if (cpu_has_feature(CPU_FTR_HVMODE) && radix_enabled()) {
- int cpu = smp_processor_id();
- int sib = cpu_first_thread_sibling(cpu);
- bool flush = false;
-
- for (; sib <= cpu_last_thread_sibling(cpu) && !flush; sib++) {
- if (sib == cpu)
- continue;
- if (!cpu_possible(sib))
- continue;
- if (paca_ptrs[sib]->kvm_hstate.kvm_vcpu)
- flush = true;
- }
- if (flush)
- _tlbiel_pid(pid, RIC_FLUSH_ALL);
- }
-}
-EXPORT_SYMBOL_GPL(radix_kvm_prefetch_workaround);
-#endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
diff --git a/arch/powerpc/mm/mmu_context.c b/arch/powerpc/mm/mmu_context.c
index 18f20da0d348..7479d39976c9 100644
--- a/arch/powerpc/mm/mmu_context.c
+++ b/arch/powerpc/mm/mmu_context.c
@@ -81,9 +81,7 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
if (cpu_has_feature(CPU_FTR_ALTIVEC))
asm volatile ("dssall");
- if (new_on_cpu)
- radix_kvm_prefetch_workaround(next);
- else
+ if (!new_on_cpu)
membarrier_arch_switch_mm(prev, next, tsk);
/*
--
2.23.0
More information about the Linuxppc-dev
mailing list