Re: [Nouveau] RFC: [PATCH] x86/kmmio: fix mmiotrace for hugepages

[Pierre Moreau]

The secondary hit exception thrown while MMIOtracing NVIDIA's driver is gone
with this patch.

Tested-by: Pierre Moreau <pierre.morrow@xxxxxxx>

On 02:03 AM - Mar 03 2016, Karol Herbst wrote:
> Because Linux might use bigger pages than the 4K pages to handle those mmio
> ioremaps, the kmmio code shouldn't rely on the pade id as it currently does.
> 
> Using the memory address instead of the page id let's us lookup how big the
> page is and what it's base address is, so that we won't get a page fault
> within the same page twice anymore.
> 
> I don't know if I got this right though, so please read this change with
> great care
> 
> v2: use page_level macros
> 
> Signed-off-by: Karol Herbst <nouveau@xxxxxxxxxxxxxx>
> ---
>  arch/x86/mm/kmmio.c | 89 ++++++++++++++++++++++++++++++++++++-----------------
>  1 file changed, 60 insertions(+), 29 deletions(-)
> 
> diff --git a/arch/x86/mm/kmmio.c b/arch/x86/mm/kmmio.c
> index 637ab34..d203beb 100644
> --- a/arch/x86/mm/kmmio.c
> +++ b/arch/x86/mm/kmmio.c
> @@ -33,7 +33,7 @@
>  struct kmmio_fault_page {
>  	struct list_head list;
>  	struct kmmio_fault_page *release_next;
> -	unsigned long page; /* location of the fault page */
> +	unsigned long addr; /* the requested address */
>  	pteval_t old_presence; /* page presence prior to arming */
>  	bool armed;
>  
> @@ -70,9 +70,16 @@ unsigned int kmmio_count;
>  static struct list_head kmmio_page_table[KMMIO_PAGE_TABLE_SIZE];
>  static LIST_HEAD(kmmio_probes);
>  
> -static struct list_head *kmmio_page_list(unsigned long page)
> +static struct list_head *kmmio_page_list(unsigned long addr)
>  {
> -	return &kmmio_page_table[hash_long(page, KMMIO_PAGE_HASH_BITS)];
> +	unsigned int l;
> +	pte_t *pte = lookup_address(addr, &l);
> +
> +	if (!pte)
> +		return NULL;
> +	addr &= page_level_mask(l);
> +
> +	return &kmmio_page_table[hash_long(addr, KMMIO_PAGE_HASH_BITS)];
>  }
>  
>  /* Accessed per-cpu */
> @@ -98,15 +105,19 @@ static struct kmmio_probe *get_kmmio_probe(unsigned long addr)
>  }
>  
>  /* You must be holding RCU read lock. */
> -static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long page)
> +static struct kmmio_fault_page *get_kmmio_fault_page(unsigned long addr)
>  {
>  	struct list_head *head;
>  	struct kmmio_fault_page *f;
> +	unsigned int l;
> +	pte_t *pte = lookup_address(addr, &l);
>  
> -	page &= PAGE_MASK;
> -	head = kmmio_page_list(page);
> +	if (!pte)
> +		return NULL;
> +	addr &= page_level_mask(l);
> +	head = kmmio_page_list(addr);
>  	list_for_each_entry_rcu(f, head, list) {
> -		if (f->page == page)
> +		if (f->addr == addr)
>  			return f;
>  	}
>  	return NULL;
> @@ -137,10 +148,10 @@ static void clear_pte_presence(pte_t *pte, bool clear, pteval_t *old)
>  static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
>  {
>  	unsigned int level;
> -	pte_t *pte = lookup_address(f->page, &level);
> +	pte_t *pte = lookup_address(f->addr, &level);
>  
>  	if (!pte) {
> -		pr_err("no pte for page 0x%08lx\n", f->page);
> +		pr_err("no pte for addr 0x%08lx\n", f->addr);
>  		return -1;
>  	}
>  
> @@ -156,7 +167,7 @@ static int clear_page_presence(struct kmmio_fault_page *f, bool clear)
>  		return -1;
>  	}
>  
> -	__flush_tlb_one(f->page);
> +	__flush_tlb_one(f->addr);
>  	return 0;
>  }
>  
> @@ -176,12 +187,12 @@ static int arm_kmmio_fault_page(struct kmmio_fault_page *f)
>  	int ret;
>  	WARN_ONCE(f->armed, KERN_ERR pr_fmt("kmmio page already armed.\n"));
>  	if (f->armed) {
> -		pr_warning("double-arm: page 0x%08lx, ref %d, old %d\n",
> -			   f->page, f->count, !!f->old_presence);
> +		pr_warning("double-arm: addr 0x%08lx, ref %d, old %d\n",
> +			   f->addr, f->count, !!f->old_presence);
>  	}
>  	ret = clear_page_presence(f, true);
> -	WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming 0x%08lx failed.\n"),
> -		  f->page);
> +	WARN_ONCE(ret < 0, KERN_ERR pr_fmt("arming at 0x%08lx failed.\n"),
> +		  f->addr);
>  	f->armed = true;
>  	return ret;
>  }
> @@ -191,7 +202,7 @@ static void disarm_kmmio_fault_page(struct kmmio_fault_page *f)
>  {
>  	int ret = clear_page_presence(f, false);
>  	WARN_ONCE(ret < 0,
> -			KERN_ERR "kmmio disarming 0x%08lx failed.\n", f->page);
> +			KERN_ERR "kmmio disarming at 0x%08lx failed.\n", f->addr);
>  	f->armed = false;
>  }
>  
> @@ -215,6 +226,12 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
>  	struct kmmio_context *ctx;
>  	struct kmmio_fault_page *faultpage;
>  	int ret = 0; /* default to fault not handled */
> +	unsigned long page_base = addr;
> +	unsigned int l;
> +	pte_t *pte = lookup_address(addr, &l);
> +	if (!pte)
> +		return -EINVAL;
> +	page_base &= page_level_mask(l);
>  
>  	/*
>  	 * Preemption is now disabled to prevent process switch during
> @@ -227,7 +244,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
>  	preempt_disable();
>  	rcu_read_lock();
>  
> -	faultpage = get_kmmio_fault_page(addr);
> +	faultpage = get_kmmio_fault_page(page_base);
>  	if (!faultpage) {
>  		/*
>  		 * Either this page fault is not caused by kmmio, or
> @@ -239,7 +256,7 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
>  
>  	ctx = &get_cpu_var(kmmio_ctx);
>  	if (ctx->active) {
> -		if (addr == ctx->addr) {
> +		if (page_base == ctx->addr) {
>  			/*
>  			 * A second fault on the same page means some other
>  			 * condition needs handling by do_page_fault(), the
> @@ -267,9 +284,9 @@ int kmmio_handler(struct pt_regs *regs, unsigned long addr)
>  	ctx->active++;
>  
>  	ctx->fpage = faultpage;
> -	ctx->probe = get_kmmio_probe(addr);
> +	ctx->probe = get_kmmio_probe(page_base);
>  	ctx->saved_flags = (regs->flags & (X86_EFLAGS_TF | X86_EFLAGS_IF));
> -	ctx->addr = addr;
> +	ctx->addr = page_base;
>  
>  	if (ctx->probe && ctx->probe->pre_handler)
>  		ctx->probe->pre_handler(ctx->probe, regs, addr);
> @@ -354,12 +371,11 @@ out:
>  }
>  
>  /* You must be holding kmmio_lock. */
> -static int add_kmmio_fault_page(unsigned long page)
> +static int add_kmmio_fault_page(unsigned long addr)
>  {
>  	struct kmmio_fault_page *f;
>  
> -	page &= PAGE_MASK;
> -	f = get_kmmio_fault_page(page);
> +	f = get_kmmio_fault_page(addr);
>  	if (f) {
>  		if (!f->count)
>  			arm_kmmio_fault_page(f);
> @@ -372,26 +388,25 @@ static int add_kmmio_fault_page(unsigned long page)
>  		return -1;
>  
>  	f->count = 1;
> -	f->page = page;
> +	f->addr = addr;
>  
>  	if (arm_kmmio_fault_page(f)) {
>  		kfree(f);
>  		return -1;
>  	}
>  
> -	list_add_rcu(&f->list, kmmio_page_list(f->page));
> +	list_add_rcu(&f->list, kmmio_page_list(f->addr));
>  
>  	return 0;
>  }
>  
>  /* You must be holding kmmio_lock. */
> -static void release_kmmio_fault_page(unsigned long page,
> +static void release_kmmio_fault_page(unsigned long addr,
>  				struct kmmio_fault_page **release_list)
>  {
>  	struct kmmio_fault_page *f;
>  
> -	page &= PAGE_MASK;
> -	f = get_kmmio_fault_page(page);
> +	f = get_kmmio_fault_page(addr);
>  	if (!f)
>  		return;
>  
> @@ -420,18 +435,27 @@ int register_kmmio_probe(struct kmmio_probe *p)
>  	int ret = 0;
>  	unsigned long size = 0;
>  	const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
> +	unsigned int l;
> +	pte_t *pte;
>  
>  	spin_lock_irqsave(&kmmio_lock, flags);
>  	if (get_kmmio_probe(p->addr)) {
>  		ret = -EEXIST;
>  		goto out;
>  	}
> +
> +	pte = lookup_address(p->addr, &l);
> +	if (!pte) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
>  	kmmio_count++;
>  	list_add_rcu(&p->list, &kmmio_probes);
>  	while (size < size_lim) {
>  		if (add_kmmio_fault_page(p->addr + size))
>  			pr_err("Unable to set page fault.\n");
> -		size += PAGE_SIZE;
> +		size += page_level_size(l);
>  	}
>  out:
>  	spin_unlock_irqrestore(&kmmio_lock, flags);
> @@ -506,11 +530,18 @@ void unregister_kmmio_probe(struct kmmio_probe *p)
>  	const unsigned long size_lim = p->len + (p->addr & ~PAGE_MASK);
>  	struct kmmio_fault_page *release_list = NULL;
>  	struct kmmio_delayed_release *drelease;
> +	unsigned int l;
> +	pte_t *pte;
> +
> +	pte = lookup_address(p->addr, &l);
> +	if (!pte) {
> +		return;
> +	}
>  
>  	spin_lock_irqsave(&kmmio_lock, flags);
>  	while (size < size_lim) {
>  		release_kmmio_fault_page(p->addr + size, &release_list);
> -		size += PAGE_SIZE;
> +		size += page_level_size(l);
>  	}
>  	list_del_rcu(&p->list);
>  	kmmio_count--;
> -- 
> 2.7.2
> 
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