Re: [RFC/PATCH v3 01/16] s390/mm: make gmap_protect_range more modular

[David Hildenbrand <david@redhat.com>]

> +/**
> + * gmap_pmd_op_walk - walk the gmap tables, get the guest table lock
> + *		      and return the pmd pointer
> + * @gmap: pointer to guest mapping meta data structure
> + * @gaddr: virtual address in the guest address space
> + *
> + * Returns a pointer to the pmd for a guest address, or NULL
> + */
> +static inline pmd_t *gmap_pmd_op_walk(struct gmap *gmap, unsigned long gaddr)
> +{
> +	pmd_t *pmdp;
> +
> +	BUG_ON(gmap_is_shadow(gmap));
> +	spin_lock(&gmap->guest_table_lock);
> +	pmdp = (pmd_t *) gmap_table_walk(gmap, gaddr, 1);
> +

So gmap_table_walk() now basically always has to be called with the
guest_table_lock held. We could add a BUG/WARN for that in
gmap_table_walk().

> +	if (!pmdp || pmd_none(*pmdp)) {
> +		spin_unlock(&gmap->guest_table_lock);
> +		return NULL;
> +	}
> +
> +	/* 4k page table entries are locked via the pte (pte_alloc_map_lock). */
> +	if (!pmd_large(*pmdp))
> +		spin_unlock(&gmap->guest_table_lock);
> +	return pmdp;
> +}
> +
> +/**
> + * gmap_pmd_op_end - release the guest_table_lock if needed
> + * @gmap: pointer to the guest mapping meta data structure
> + * @pmdp: pointer to the pmd
> + */
> +static inline void gmap_pmd_op_end(struct gmap *gmap, pmd_t *pmdp)
> +{
> +	if (pmd_large(*pmdp))
> +		spin_unlock(&gmap->guest_table_lock);
> +}
> +
> +/*
> + * gmap_protect_pte - remove access rights to memory and set pgste bits
> + * @gmap: pointer to guest mapping meta data structure
> + * @gaddr: virtual address in the guest address space
> + * @pmdp: pointer to the pmd associated with the pte
> + * @prot: indicates access rights: PROT_NONE, PROT_READ or PROT_WRITE
> + * @bits: pgste notification bits to set
> + *
> + * Returns 0 if successfully protected, -ENOMEM if out of memory and
> + * -EAGAIN if a fixup is needed.
> + *
> + * Expected to be called with sg->mm->mmap_sem in read and
> + * guest_table_lock held for shadow gmaps.
> + */

stale comment about shadow gmaps.

> +static int gmap_protect_pte(struct gmap *gmap, unsigned long gaddr,
> +			    pmd_t *pmdp, int prot, unsigned long bits)
> +{
> +	int rc;
> +	pte_t *ptep;
> +	spinlock_t *ptl = NULL;
> +
> +	ptep = pte_alloc_map_lock(gmap->mm, pmdp, gaddr, &ptl);
> +	if (!ptep)
> +		return -ENOMEM;
> +
> +	/* Protect and unlock. */
> +	rc = ptep_force_prot(gmap->mm, gaddr, ptep, prot, bits);
> +	gmap_pte_op_end(ptl);
> +	return rc;
>  }
>  
>  /*
> @@ -896,16 +966,20 @@ static int gmap_protect_range(struct gmap *gmap, unsigned long gaddr,
>  			      unsigned long len, int prot, unsigned long bits)
>  {
>  	unsigned long vmaddr;
> -	spinlock_t *ptl;
> -	pte_t *ptep;
> +	pmd_t *pmdp;
>  	int rc;
>  
>  	while (len) {
>  		rc = -EAGAIN;
> -		ptep = gmap_pte_op_walk(gmap, gaddr, &ptl);
> -		if (ptep) {
> -			rc = ptep_force_prot(gmap->mm, gaddr, ptep, prot, bits);
> -			gmap_pte_op_end(ptl);
> +		pmdp = gmap_pmd_op_walk(gmap, gaddr);
> +		if (pmdp && !(pmd_val(*pmdp) & _SEGMENT_ENTRY_INVALID)) {

You could move the !(pmd_val(*pmdp) & _SEGMENT_ENTRY_INVALID) check into
either gmap_pmd_op_walk() or gmap_protect_pte(). Makes this easier to
read (and you already have similar checks in gmap_pmd_op_walk() )

> +			rc = gmap_protect_pte(gmap, gaddr, pmdp, prot,
> +					      bits);
> +			if (!rc) {
> +				len -= PAGE_SIZE;
> +				gaddr += PAGE_SIZE;
> +			}
> +			gmap_pmd_op_end(gmap, pmdp);
>  		}
>  		if (rc) {
>  			vmaddr = __gmap_translate(gmap, gaddr);
> @@ -914,10 +988,7 @@ static int gmap_protect_range(struct gmap *gmap, unsigned long gaddr,
>  			rc = gmap_pte_op_fixup(gmap, gaddr, vmaddr, prot);
>  			if (rc)
>  				return rc;
> -			continue;
>  		}
> -		gaddr += PAGE_SIZE;
> -		len -= PAGE_SIZE;
>  	}
>  	return 0;
>  }
> 

Apart from that, looks good to me.

-- 

Thanks,

David / dhildenb