On 12/30/24 09:53, Rik van Riel wrote:
...
> +#ifdef CONFIG_CPU_SUP_AMD
> + struct list_head broadcast_asid_list;
> + u16 broadcast_asid;
> + bool asid_transition;
> +#endif
Could we either do:
config X86_TLB_FLUSH_BROADCAST_HW
bool
depends on CONFIG_CPU_SUP_AMD
or even
#define X86_TLB_FLUSH_BROADCAST_HW CONFIG_CPU_SUP_AMD
for the whole series please?
There are a non-trivial number of #ifdefs here and it would be nice to
know what there're for, logically.
This is a completely selfish request because Intel has a similar feature
and we're surely going to give this approach a try on Intel CPUs too.
Second, is there something that prevents you from defining a new
MM_CONTEXT_* flag instead of a new bool? It might save bloating the
context by a few words.
> #ifdef CONFIG_ADDRESS_MASKING
> /* Active LAM mode: X86_CR3_LAM_U48 or X86_CR3_LAM_U57 or 0 (disabled) */
> unsigned long lam_cr3_mask;
> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
> index 795fdd53bd0a..0dc446c427d2 100644
> --- a/arch/x86/include/asm/mmu_context.h
> +++ b/arch/x86/include/asm/mmu_context.h
> @@ -139,6 +139,8 @@ static inline void mm_reset_untag_mask(struct mm_struct *mm)
> #define enter_lazy_tlb enter_lazy_tlb
> extern void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
>
> +extern void destroy_context_free_broadcast_asid(struct mm_struct *mm);
> +
> /*
> * Init a new mm. Used on mm copies, like at fork()
> * and on mm's that are brand-new, like at execve().
> @@ -161,6 +163,13 @@ static inline int init_new_context(struct task_struct *tsk,
> mm->context.execute_only_pkey = -1;
> }
> #endif
> +
> +#ifdef CONFIG_CPU_SUP_AMD
> + INIT_LIST_HEAD(&mm->context.broadcast_asid_list);
> + mm->context.broadcast_asid = 0;
> + mm->context.asid_transition = false;
> +#endif
We've been inconsistent about it, but I think I'd prefer that this had a:
if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) {
...
}
wrapper as opposed to CONFIG_CPU_SUP_AMD. It might save dirtying a
cacheline on all the CPUs that don't care. cpu_feature_enabled() would
also function the same as the #ifdef.
> mm_reset_untag_mask(mm);
> init_new_context_ldt(mm);
> return 0;
> @@ -170,6 +179,9 @@ static inline int init_new_context(struct task_struct *tsk,
> static inline void destroy_context(struct mm_struct *mm)
> {
> destroy_context_ldt(mm);
> +#ifdef CONFIG_CPU_SUP_AMD
> + destroy_context_free_broadcast_asid(mm);
> +#endif
> }
>
> extern void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index 20074f17fbcd..5e9956af98d1 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -65,6 +65,23 @@ static inline void cr4_clear_bits(unsigned long mask)
> */
> #define TLB_NR_DYN_ASIDS 6
>
> +#ifdef CONFIG_CPU_SUP_AMD
> +#define is_dyn_asid(asid) (asid) < TLB_NR_DYN_ASIDS
> +#define is_broadcast_asid(asid) (asid) >= TLB_NR_DYN_ASIDS
> +#define in_asid_transition(info) (info->mm && info->mm->context.asid_transition)
> +#define mm_broadcast_asid(mm) (mm->context.broadcast_asid)
> +#else
> +#define is_dyn_asid(asid) true
> +#define is_broadcast_asid(asid) false
> +#define in_asid_transition(info) false
> +#define mm_broadcast_asid(mm) 0
I think it was said elsewhere, but I also prefer static inlines for
these instead of macros. The type checking that you get from the
compiler in _both_ compile configurations is much more valuable than
brevity.
...
> + /*
> + * TLB consistency for this ASID is maintained with INVLPGB;
> + * TLB flushes happen even while the process isn't running.
> + */
I'm not sure this comment helps much. The thing that matters here is
that a broadcast ASID is asigned from a global namespace and not from a
per-cpu namespace.
> +#ifdef CONFIG_CPU_SUP_AMD
> + if (static_cpu_has(X86_FEATURE_INVLPGB) && mm_broadcast_asid(next)) {
> + *new_asid = mm_broadcast_asid(next);
> + *need_flush = false;
> + return;
> + }
> +#endif
> +
> if (this_cpu_read(cpu_tlbstate.invalidate_other))
> clear_asid_other();
>
> @@ -251,6 +265,245 @@ static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
> *need_flush = true;
> }
>
> +#ifdef CONFIG_CPU_SUP_AMD
> +/*
> + * Logic for AMD INVLPGB support.
> + */
This comment is another indication that this shouldn't all be crammed
under CONFIG_CPU_SUP_AMD.
> +static DEFINE_RAW_SPINLOCK(broadcast_asid_lock);
> +static u16 last_broadcast_asid = TLB_NR_DYN_ASIDS;
> +static DECLARE_BITMAP(broadcast_asid_used, MAX_ASID_AVAILABLE) = { 0 };
I'm debating whether this should be a bitmap for "broadcast" ASIDs alone
or for all ASIDs.
> +static LIST_HEAD(broadcast_asid_list);
> +static int broadcast_asid_available = MAX_ASID_AVAILABLE - TLB_NR_DYN_ASIDS - 1;
> +
> +static void reset_broadcast_asid_space(void)
> +{
> + mm_context_t *context;
> +
> + lockdep_assert_held(&broadcast_asid_lock);
> +
> + /*
> + * Flush once when we wrap around the ASID space, so we won't need
> + * to flush every time we allocate an ASID for boradcast flushing.
^ broadcast
> + */
> + invlpgb_flush_all_nonglobals();
> + tlbsync();
> +
> + /*
> + * Leave the currently used broadcast ASIDs set in the bitmap, since
> + * those cannot be reused before the next wraparound and flush..
> + */
> + bitmap_clear(broadcast_asid_used, 0, MAX_ASID_AVAILABLE);
> + list_for_each_entry(context, &broadcast_asid_list, broadcast_asid_list)
> + __set_bit(context->broadcast_asid, broadcast_asid_used);
> +
> + last_broadcast_asid = TLB_NR_DYN_ASIDS;
> +}
'TLB_NR_DYN_ASIDS' is special here. Could it please be made more clear
what it means *logically*?
> +static u16 get_broadcast_asid(void)
> +{
> + lockdep_assert_held(&broadcast_asid_lock);
> +
> + do {
> + u16 start = last_broadcast_asid;
> + u16 asid = find_next_zero_bit(broadcast_asid_used, MAX_ASID_AVAILABLE, start);
> +
> + if (asid >= MAX_ASID_AVAILABLE) {
> + reset_broadcast_asid_space();
> + continue;
> + }
> +
> + /* Try claiming this broadcast ASID. */
> + if (!test_and_set_bit(asid, broadcast_asid_used)) {
> + last_broadcast_asid = asid;
> + return asid;
> + }
> + } while (1);
> +}
I think it was said elsewhere, but the "try" logic doesn't make a lot of
sense to me when it's all protected by a global lock.
> +/*
> + * Returns true if the mm is transitioning from a CPU-local ASID to a broadcast
> + * (INVLPGB) ASID, or the other way around.
> + */
> +static bool needs_broadcast_asid_reload(struct mm_struct *next, u16 prev_asid)
> +{
> + u16 broadcast_asid = mm_broadcast_asid(next);
> +
> + if (broadcast_asid && prev_asid != broadcast_asid)
> + return true;
> +
> + if (!broadcast_asid && is_broadcast_asid(prev_asid))
> + return true;
> +
> + return false;
> +}
> +
> +void destroy_context_free_broadcast_asid(struct mm_struct *mm)
> +{
> + if (!mm->context.broadcast_asid)
> + return;
> +
> + guard(raw_spinlock_irqsave)(&broadcast_asid_lock);
> + mm->context.broadcast_asid = 0;
> + list_del(&mm->context.broadcast_asid_list);
> + broadcast_asid_available++;
> +}
> +
> +static bool mm_active_cpus_exceeds(struct mm_struct *mm, int threshold)
> +{
This function is pretty important. It's kinda missing a comment about
its theory of operation.
> + int count = 0;
> + int cpu;
> +
> + if (cpumask_weight(mm_cpumask(mm)) <= threshold)
> + return false;
There's a lot of potential redundancy between this check and the one
below. I assume this sequence was desinged for performance: first, do a
cheap, one-stop-shopping check on mm_cpumask(). If it looks, ok, then go
marauding around in a bunch of per_cpu() cachelines in a much more
expensive but precise search.
Could we spell some of that out explicitly, please?
> + for_each_cpu(cpu, mm_cpumask(mm)) {
> + /* Skip the CPUs that aren't really running this process. */
> + if (per_cpu(cpu_tlbstate.loaded_mm, cpu) != mm)
> + continue;
This is the only place I know of where 'cpu_tlbstate' is read from a
non-local CPU. This is fundamentally racy as hell and needs some heavy
commenting about why this raciness is OK.
