On Mon, Dec 2, 2019 at 2:08 PM Jordan Niethe <jniet...@gmail.com> wrote:
>
> Commit a25bd72badfa ("powerpc/mm/radix: Workaround prefetch issue with
> KVM") introduced a number of workarounds as coming out of a guest with
> the mmu enabled would make the cpu would start running in hypervisor
> state with the PID value from the guest. The cpu will then start
> prefetching for the hypervisor with that PID value.
>
> In Power9 DD2.2 the cpu behaviour was modified to fix this. When
> accessing Quadrant 0 in hypervisor mode with LPID != 0 prefetching will
> not be performed. This means that we can get rid of the workarounds for
> Power9 DD2.2 and later revisions.
>
> Signed-off-by: Jordan Niethe <jniet...@gmail.com>
> ---
> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 9 +++++++++
> arch/powerpc/mm/book3s64/radix_pgtable.c | 18 ++++++++++++------
> arch/powerpc/mm/book3s64/radix_tlb.c | 5 +++++
> 3 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> index faebcbb8c4db..6bbc5fbc7ea9 100644
> --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> @@ -1793,6 +1793,15 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
> tlbsync
> ptesync
>
> + /* We do not need this work around from POWER9 DD2.2 and onwards */
> + mfspr r3, SPRN_PVR
> + srwi r6, r3, 16
> + cmpwi cr0, r6, PVR_POWER9
> + bne cr0, 2f
> + andi. r3, r3, 0xfff
> + cmpwi cr0, r3, 0x202
> + bge cr0, 2f
This seems like the sort of thing we'd want to use a CPU_FTR_SECTION()
for. We probably want to have a CPU_FTR for this anyway so we're not
open-coding the PVR check all over the place.
> +
> /* Radix: Handle the case where the guest used an illegal PID */
> LOAD_REG_ADDR(r4, mmu_base_pid)
> lwz r3, VCPU_GUEST_PID(r9)
> diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c
> b/arch/powerpc/mm/book3s64/radix_pgtable.c
> index 6ee17d09649c..1f280124994e 100644
> --- a/arch/powerpc/mm/book3s64/radix_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
> @@ -312,6 +312,7 @@ static void __init radix_init_pgtable(void)
> {
> unsigned long rts_field;
> struct memblock_region *reg;
> + unsigned int pvr;
>
> /* We don't support slb for radix */
> mmu_slb_size = 0;
> @@ -336,24 +337,29 @@ static void __init radix_init_pgtable(void)
> }
>
> /* Find out how many PID bits are supported */
> + pvr = mfspr(SPRN_PVR);
> if (cpu_has_feature(CPU_FTR_HVMODE)) {
> if (!mmu_pid_bits)
> mmu_pid_bits = 20;
> #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> /*
> - * 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
> + * Before Power9 DD2.2, 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
> */
> - mmu_base_pid = 1 << (mmu_pid_bits - 1);
> + if (PVR_VER(pvr) == PVR_POWER9 && ((0xfff & pvr) < 0x202))
> + mmu_base_pid = 1;
> + else
> + 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_pid_bits = (PVR_VER(pvr) == PVR_POWER9 &&
> + ((0xfff & pvr) < 0x202)) ? 19 : 20;
> mmu_base_pid = 1;
> }
>
> diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c
> b/arch/powerpc/mm/book3s64/radix_tlb.c
> index 67af871190c6..cc86d8a88b86 100644
> --- a/arch/powerpc/mm/book3s64/radix_tlb.c
> +++ b/arch/powerpc/mm/book3s64/radix_tlb.c
> @@ -1217,10 +1217,15 @@ void radix__flush_tlb_all(void)
> extern void radix_kvm_prefetch_workaround(struct mm_struct *mm)
> {
> unsigned long pid = mm->context.id;
> + unsigned int pvr;
>
> if (unlikely(pid == MMU_NO_CONTEXT))
> return;
>
> + pvr = mfspr(SPRN_PVR);
> + if (PVR_VER(pvr) != PVR_POWER9 || ((0xfff & pvr) >= 0x202))
> + 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
> --
> 2.20.1
>
