| Message ID | 20230722022251.3446223-13-rananta@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: arm64: Add support for FEAT_TLBIRANGE | expand |
On Sat, 22 Jul 2023 03:22:51 +0100, Raghavendra Rao Ananta <rananta@google.com> wrote: > > The current implementation of the stage-2 unmap walker traverses > the given range and, as a part of break-before-make, performs > TLB invalidations with a DSB for every PTE. A multitude of this > combination could cause a performance bottleneck on some systems. > > Hence, if the system supports FEAT_TLBIRANGE, defer the TLB > invalidations until the entire walk is finished, and then > use range-based instructions to invalidate the TLBs in one go. > Condition deferred TLB invalidation on the system supporting FWB, > as the optimization is entirely pointless when the unmap walker > needs to perform CMOs. > > Rename stage2_put_pte() to stage2_unmap_put_pte() as the function > now serves the stage-2 unmap walker specifically, rather than > acting generic. > > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com> > --- > arch/arm64/kvm/hyp/pgtable.c | 67 +++++++++++++++++++++++++++++++----- > 1 file changed, 58 insertions(+), 9 deletions(-) > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > index 5ef098af1736..cf88933a2ea0 100644 > --- a/arch/arm64/kvm/hyp/pgtable.c > +++ b/arch/arm64/kvm/hyp/pgtable.c > @@ -831,16 +831,54 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n > smp_store_release(ctx->ptep, new); > } > > -static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu, > - struct kvm_pgtable_mm_ops *mm_ops) > +struct stage2_unmap_data { > + struct kvm_pgtable *pgt; > + bool defer_tlb_flush_init; > +}; > + > +static bool __stage2_unmap_defer_tlb_flush(struct kvm_pgtable *pgt) > +{ > + /* > + * If FEAT_TLBIRANGE is implemented, defer the individual > + * TLB invalidations until the entire walk is finished, and > + * then use the range-based TLBI instructions to do the > + * invalidations. Condition deferred TLB invalidation on the > + * system supporting FWB, as the optimization is entirely > + * pointless when the unmap walker needs to perform CMOs. > + */ > + return system_supports_tlb_range() && stage2_has_fwb(pgt); > +} > + > +static bool stage2_unmap_defer_tlb_flush(struct stage2_unmap_data *unmap_data) > +{ > + bool defer_tlb_flush = __stage2_unmap_defer_tlb_flush(unmap_data->pgt); > + > + /* > + * Since __stage2_unmap_defer_tlb_flush() is based on alternative > + * patching and the TLBIs' operations behavior depend on this, > + * track if there's any change in the state during the unmap sequence. > + */ > + WARN_ON(unmap_data->defer_tlb_flush_init != defer_tlb_flush); > + return defer_tlb_flush; I really don't understand what you're testing here. The ability to defer TLB invalidation is a function of the system capabilities (range+FWB) and a single flag that is only set on the host for pKVM. How could that change in the middle of the life of the system? if further begs the question about the need for the unmap_data data structure. It looks to me that we could simply pass the pgt pointer around and be done with it. Am I missing something obvious? M.
On Thu, Jul 27, 2023 at 6:12 AM Marc Zyngier <maz@kernel.org> wrote: > > On Sat, 22 Jul 2023 03:22:51 +0100, > Raghavendra Rao Ananta <rananta@google.com> wrote: > > > > The current implementation of the stage-2 unmap walker traverses > > the given range and, as a part of break-before-make, performs > > TLB invalidations with a DSB for every PTE. A multitude of this > > combination could cause a performance bottleneck on some systems. > > > > Hence, if the system supports FEAT_TLBIRANGE, defer the TLB > > invalidations until the entire walk is finished, and then > > use range-based instructions to invalidate the TLBs in one go. > > Condition deferred TLB invalidation on the system supporting FWB, > > as the optimization is entirely pointless when the unmap walker > > needs to perform CMOs. > > > > Rename stage2_put_pte() to stage2_unmap_put_pte() as the function > > now serves the stage-2 unmap walker specifically, rather than > > acting generic. > > > > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com> > > --- > > arch/arm64/kvm/hyp/pgtable.c | 67 +++++++++++++++++++++++++++++++----- > > 1 file changed, 58 insertions(+), 9 deletions(-) > > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index 5ef098af1736..cf88933a2ea0 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -831,16 +831,54 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n > > smp_store_release(ctx->ptep, new); > > } > > > > -static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu, > > - struct kvm_pgtable_mm_ops *mm_ops) > > +struct stage2_unmap_data { > > + struct kvm_pgtable *pgt; > > + bool defer_tlb_flush_init; > > +}; > > + > > +static bool __stage2_unmap_defer_tlb_flush(struct kvm_pgtable *pgt) > > +{ > > + /* > > + * If FEAT_TLBIRANGE is implemented, defer the individual > > + * TLB invalidations until the entire walk is finished, and > > + * then use the range-based TLBI instructions to do the > > + * invalidations. Condition deferred TLB invalidation on the > > + * system supporting FWB, as the optimization is entirely > > + * pointless when the unmap walker needs to perform CMOs. > > + */ > > + return system_supports_tlb_range() && stage2_has_fwb(pgt); > > +} > > + > > +static bool stage2_unmap_defer_tlb_flush(struct stage2_unmap_data *unmap_data) > > +{ > > + bool defer_tlb_flush = __stage2_unmap_defer_tlb_flush(unmap_data->pgt); > > + > > + /* > > + * Since __stage2_unmap_defer_tlb_flush() is based on alternative > > + * patching and the TLBIs' operations behavior depend on this, > > + * track if there's any change in the state during the unmap sequence. > > + */ > > + WARN_ON(unmap_data->defer_tlb_flush_init != defer_tlb_flush); > > + return defer_tlb_flush; > > I really don't understand what you're testing here. The ability to > defer TLB invalidation is a function of the system capabilities > (range+FWB) and a single flag that is only set on the host for pKVM. > > How could that change in the middle of the life of the system? if > further begs the question about the need for the unmap_data data > structure. > > It looks to me that we could simply pass the pgt pointer around and be > done with it. Am I missing something obvious? > From one of the previous comments [1] (used in a different context), I'm given to understand that since these feature checks are governed by alternative patching, they can potentially change (at runtime?). Is that not the case and I have misunderstood the idea in comment [1] entirely? Is it solely used for optimization purposes and set only once? If that's the case, I can get rid of the WARN_ON() and unmap_data. - Raghavendra [1]: https://lore.kernel.org/all/ZGPPj1AXS0Uah2Ug@linux.dev/ > M. > > -- > Without deviation from the norm, progress is not possible.
On Mon, 31 Jul 2023 19:26:09 +0100, Raghavendra Rao Ananta <rananta@google.com> wrote: > > On Thu, Jul 27, 2023 at 6:12 AM Marc Zyngier <maz@kernel.org> wrote: > > > > On Sat, 22 Jul 2023 03:22:51 +0100, > > Raghavendra Rao Ananta <rananta@google.com> wrote: > > > > > > The current implementation of the stage-2 unmap walker traverses > > > the given range and, as a part of break-before-make, performs > > > TLB invalidations with a DSB for every PTE. A multitude of this > > > combination could cause a performance bottleneck on some systems. > > > > > > Hence, if the system supports FEAT_TLBIRANGE, defer the TLB > > > invalidations until the entire walk is finished, and then > > > use range-based instructions to invalidate the TLBs in one go. > > > Condition deferred TLB invalidation on the system supporting FWB, > > > as the optimization is entirely pointless when the unmap walker > > > needs to perform CMOs. > > > > > > Rename stage2_put_pte() to stage2_unmap_put_pte() as the function > > > now serves the stage-2 unmap walker specifically, rather than > > > acting generic. > > > > > > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com> > > > --- > > > arch/arm64/kvm/hyp/pgtable.c | 67 +++++++++++++++++++++++++++++++----- > > > 1 file changed, 58 insertions(+), 9 deletions(-) > > > > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > > index 5ef098af1736..cf88933a2ea0 100644 > > > --- a/arch/arm64/kvm/hyp/pgtable.c > > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > > @@ -831,16 +831,54 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n > > > smp_store_release(ctx->ptep, new); > > > } > > > > > > -static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu, > > > - struct kvm_pgtable_mm_ops *mm_ops) > > > +struct stage2_unmap_data { > > > + struct kvm_pgtable *pgt; > > > + bool defer_tlb_flush_init; > > > +}; > > > + > > > +static bool __stage2_unmap_defer_tlb_flush(struct kvm_pgtable *pgt) > > > +{ > > > + /* > > > + * If FEAT_TLBIRANGE is implemented, defer the individual > > > + * TLB invalidations until the entire walk is finished, and > > > + * then use the range-based TLBI instructions to do the > > > + * invalidations. Condition deferred TLB invalidation on the > > > + * system supporting FWB, as the optimization is entirely > > > + * pointless when the unmap walker needs to perform CMOs. > > > + */ > > > + return system_supports_tlb_range() && stage2_has_fwb(pgt); > > > +} > > > + > > > +static bool stage2_unmap_defer_tlb_flush(struct stage2_unmap_data *unmap_data) > > > +{ > > > + bool defer_tlb_flush = __stage2_unmap_defer_tlb_flush(unmap_data->pgt); > > > + > > > + /* > > > + * Since __stage2_unmap_defer_tlb_flush() is based on alternative > > > + * patching and the TLBIs' operations behavior depend on this, > > > + * track if there's any change in the state during the unmap sequence. > > > + */ > > > + WARN_ON(unmap_data->defer_tlb_flush_init != defer_tlb_flush); > > > + return defer_tlb_flush; > > > > I really don't understand what you're testing here. The ability to > > defer TLB invalidation is a function of the system capabilities > > (range+FWB) and a single flag that is only set on the host for pKVM. > > > > How could that change in the middle of the life of the system? if > > further begs the question about the need for the unmap_data data > > structure. > > > > It looks to me that we could simply pass the pgt pointer around and be > > done with it. Am I missing something obvious? > > > From one of the previous comments [1] (used in a different context), > I'm given to understand that since these feature checks are governed > by alternative patching, they can potentially change (at runtime?). Is > that not the case and I have misunderstood the idea in comment [1] > entirely? Is it solely used for optimization purposes and set only > once? Alternative patching, just like the static branches used to implement the capability stuff, is a one way street. At the point where KVM is initialised, these configurations are set in stone, and there is no going back. > If that's the case, I can get rid of the WARN_ON() and unmap_data. yes, please. Thanks, M.
On Wed, Aug 2, 2023 at 4:28 PM Marc Zyngier <maz@kernel.org> wrote: > > On Mon, 31 Jul 2023 19:26:09 +0100, > Raghavendra Rao Ananta <rananta@google.com> wrote: > > > > On Thu, Jul 27, 2023 at 6:12 AM Marc Zyngier <maz@kernel.org> wrote: > > > > > > On Sat, 22 Jul 2023 03:22:51 +0100, > > > Raghavendra Rao Ananta <rananta@google.com> wrote: > > > > > > > > The current implementation of the stage-2 unmap walker traverses > > > > the given range and, as a part of break-before-make, performs > > > > TLB invalidations with a DSB for every PTE. A multitude of this > > > > combination could cause a performance bottleneck on some systems. > > > > > > > > Hence, if the system supports FEAT_TLBIRANGE, defer the TLB > > > > invalidations until the entire walk is finished, and then > > > > use range-based instructions to invalidate the TLBs in one go. > > > > Condition deferred TLB invalidation on the system supporting FWB, > > > > as the optimization is entirely pointless when the unmap walker > > > > needs to perform CMOs. > > > > > > > > Rename stage2_put_pte() to stage2_unmap_put_pte() as the function > > > > now serves the stage-2 unmap walker specifically, rather than > > > > acting generic. > > > > > > > > Signed-off-by: Raghavendra Rao Ananta <rananta@google.com> > > > > --- > > > > arch/arm64/kvm/hyp/pgtable.c | 67 +++++++++++++++++++++++++++++++----- > > > > 1 file changed, 58 insertions(+), 9 deletions(-) > > > > > > > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > > > index 5ef098af1736..cf88933a2ea0 100644 > > > > --- a/arch/arm64/kvm/hyp/pgtable.c > > > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > > > @@ -831,16 +831,54 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n > > > > smp_store_release(ctx->ptep, new); > > > > } > > > > > > > > -static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu, > > > > - struct kvm_pgtable_mm_ops *mm_ops) > > > > +struct stage2_unmap_data { > > > > + struct kvm_pgtable *pgt; > > > > + bool defer_tlb_flush_init; > > > > +}; > > > > + > > > > +static bool __stage2_unmap_defer_tlb_flush(struct kvm_pgtable *pgt) > > > > +{ > > > > + /* > > > > + * If FEAT_TLBIRANGE is implemented, defer the individual > > > > + * TLB invalidations until the entire walk is finished, and > > > > + * then use the range-based TLBI instructions to do the > > > > + * invalidations. Condition deferred TLB invalidation on the > > > > + * system supporting FWB, as the optimization is entirely > > > > + * pointless when the unmap walker needs to perform CMOs. > > > > + */ > > > > + return system_supports_tlb_range() && stage2_has_fwb(pgt); > > > > +} > > > > + > > > > +static bool stage2_unmap_defer_tlb_flush(struct stage2_unmap_data *unmap_data) > > > > +{ > > > > + bool defer_tlb_flush = __stage2_unmap_defer_tlb_flush(unmap_data->pgt); > > > > + > > > > + /* > > > > + * Since __stage2_unmap_defer_tlb_flush() is based on alternative > > > > + * patching and the TLBIs' operations behavior depend on this, > > > > + * track if there's any change in the state during the unmap sequence. > > > > + */ > > > > + WARN_ON(unmap_data->defer_tlb_flush_init != defer_tlb_flush); > > > > + return defer_tlb_flush; > > > > > > I really don't understand what you're testing here. The ability to > > > defer TLB invalidation is a function of the system capabilities > > > (range+FWB) and a single flag that is only set on the host for pKVM. > > > > > > How could that change in the middle of the life of the system? if > > > further begs the question about the need for the unmap_data data > > > structure. > > > > > > It looks to me that we could simply pass the pgt pointer around and be > > > done with it. Am I missing something obvious? > > > > > From one of the previous comments [1] (used in a different context), > > I'm given to understand that since these feature checks are governed > > by alternative patching, they can potentially change (at runtime?). Is > > that not the case and I have misunderstood the idea in comment [1] > > entirely? Is it solely used for optimization purposes and set only > > once? > > Alternative patching, just like the static branches used to implement > the capability stuff, is a one way street. At the point where KVM is > initialised, these configurations are set in stone, and there is no > going back. > Understood. > > If that's the case, I can get rid of the WARN_ON() and unmap_data. > > yes, please. > Sure, I'll get rid of the WARN_ON and 'struct stage2_unmap_data' in v8. Thanks, Raghavendra > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible.
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c index 5ef098af1736..cf88933a2ea0 100644 --- a/arch/arm64/kvm/hyp/pgtable.c +++ b/arch/arm64/kvm/hyp/pgtable.c @@ -831,16 +831,54 @@ static void stage2_make_pte(const struct kvm_pgtable_visit_ctx *ctx, kvm_pte_t n smp_store_release(ctx->ptep, new); } -static void stage2_put_pte(const struct kvm_pgtable_visit_ctx *ctx, struct kvm_s2_mmu *mmu, - struct kvm_pgtable_mm_ops *mm_ops) +struct stage2_unmap_data { + struct kvm_pgtable *pgt; + bool defer_tlb_flush_init; +}; + +static bool __stage2_unmap_defer_tlb_flush(struct kvm_pgtable *pgt) +{ + /* + * If FEAT_TLBIRANGE is implemented, defer the individual + * TLB invalidations until the entire walk is finished, and + * then use the range-based TLBI instructions to do the + * invalidations. Condition deferred TLB invalidation on the + * system supporting FWB, as the optimization is entirely + * pointless when the unmap walker needs to perform CMOs. + */ + return system_supports_tlb_range() && stage2_has_fwb(pgt); +} + +static bool stage2_unmap_defer_tlb_flush(struct stage2_unmap_data *unmap_data) +{ + bool defer_tlb_flush = __stage2_unmap_defer_tlb_flush(unmap_data->pgt); + + /* + * Since __stage2_unmap_defer_tlb_flush() is based on alternative + * patching and the TLBIs' operations behavior depend on this, + * track if there's any change in the state during the unmap sequence. + */ + WARN_ON(unmap_data->defer_tlb_flush_init != defer_tlb_flush); + return defer_tlb_flush; +} + +static void stage2_unmap_put_pte(const struct kvm_pgtable_visit_ctx *ctx, + struct kvm_s2_mmu *mmu, + struct kvm_pgtable_mm_ops *mm_ops) { + struct stage2_unmap_data *unmap_data = ctx->arg; + /* - * Clear the existing PTE, and perform break-before-make with - * TLB maintenance if it was valid. + * Clear the existing PTE, and perform break-before-make if it was + * valid. Depending on the system support, the TLB maintenance for + * the same can be deferred until the entire unmap is completed. */ if (kvm_pte_valid(ctx->old)) { kvm_clear_pte(ctx->ptep); - kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, ctx->addr, ctx->level); + + if (!stage2_unmap_defer_tlb_flush(unmap_data)) + kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, mmu, + ctx->addr, ctx->level); } mm_ops->put_page(ctx->ptep); @@ -1070,7 +1108,8 @@ int kvm_pgtable_stage2_set_owner(struct kvm_pgtable *pgt, u64 addr, u64 size, static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx, enum kvm_pgtable_walk_flags visit) { - struct kvm_pgtable *pgt = ctx->arg; + struct stage2_unmap_data *unmap_data = ctx->arg; + struct kvm_pgtable *pgt = unmap_data->pgt; struct kvm_s2_mmu *mmu = pgt->mmu; struct kvm_pgtable_mm_ops *mm_ops = ctx->mm_ops; kvm_pte_t *childp = NULL; @@ -1098,7 +1137,7 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx, * block entry and rely on the remaining portions being faulted * back lazily. */ - stage2_put_pte(ctx, mmu, mm_ops); + stage2_unmap_put_pte(ctx, mmu, mm_ops); if (need_flush && mm_ops->dcache_clean_inval_poc) mm_ops->dcache_clean_inval_poc(kvm_pte_follow(ctx->old, mm_ops), @@ -1112,13 +1151,23 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx, int kvm_pgtable_stage2_unmap(struct kvm_pgtable *pgt, u64 addr, u64 size) { + int ret; + struct stage2_unmap_data unmap_data = { + .pgt = pgt, + .defer_tlb_flush_init = __stage2_unmap_defer_tlb_flush(pgt), + }; struct kvm_pgtable_walker walker = { .cb = stage2_unmap_walker, - .arg = pgt, + .arg = &unmap_data, .flags = KVM_PGTABLE_WALK_LEAF | KVM_PGTABLE_WALK_TABLE_POST, }; - return kvm_pgtable_walk(pgt, addr, size, &walker); + ret = kvm_pgtable_walk(pgt, addr, size, &walker); + if (stage2_unmap_defer_tlb_flush(&unmap_data)) + /* Perform the deferred TLB invalidations */ + kvm_tlb_flush_vmid_range(pgt->mmu, addr, size); + + return ret; } struct stage2_attr_data {
The current implementation of the stage-2 unmap walker traverses the given range and, as a part of break-before-make, performs TLB invalidations with a DSB for every PTE. A multitude of this combination could cause a performance bottleneck on some systems. Hence, if the system supports FEAT_TLBIRANGE, defer the TLB invalidations until the entire walk is finished, and then use range-based instructions to invalidate the TLBs in one go. Condition deferred TLB invalidation on the system supporting FWB, as the optimization is entirely pointless when the unmap walker needs to perform CMOs. Rename stage2_put_pte() to stage2_unmap_put_pte() as the function now serves the stage-2 unmap walker specifically, rather than acting generic. Signed-off-by: Raghavendra Rao Ananta <rananta@google.com> --- arch/arm64/kvm/hyp/pgtable.c | 67 +++++++++++++++++++++++++++++++----- 1 file changed, 58 insertions(+), 9 deletions(-)