Re: [RFC 08/14] s390/mm: Make gmap_read_table EDAT1 compatible

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On 19/09/2018 10:47, Janosch Frank wrote:
> For the upcoming support of VSIE guests on huge page backed hosts, we
> need to be able to read from large segments.
> 
> Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
> ---
>  arch/s390/mm/gmap.c | 43 ++++++++++++++++++++++++++-----------------
>  1 file changed, 26 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 26cc6ce19afb..ba0425f1c2c0 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -1274,35 +1274,44 @@ EXPORT_SYMBOL_GPL(gmap_mprotect_notify);
>  int gmap_read_table(struct gmap *gmap, unsigned long gaddr, unsigned long *val)
>  {
>  	unsigned long address, vmaddr;
> -	spinlock_t *ptl;
> +	spinlock_t *ptl_pmd = NULL, *ptl_pte = NULL;
> +	pmd_t *pmdp;
>  	pte_t *ptep, pte;
>  	int rc;
>  
> -	if (gmap_is_shadow(gmap))
> -		return -EINVAL;
> +	BUG_ON(gmap_is_shadow(gmap));

Why this change? This is documented behavior (and this is an exported
function - I think we should keep performing validity checks on exported
functions).

>  
>  	while (1) {
>  		rc = -EAGAIN;
> -		ptep = gmap_pte_op_walk(gmap, gaddr, &ptl);
> -		if (ptep) {
> -			pte = *ptep;
> -			if (pte_present(pte) && (pte_val(pte) & _PAGE_READ)) {
> -				address = pte_val(pte) & PAGE_MASK;
> -				address += gaddr & ~PAGE_MASK;
> +		vmaddr = __gmap_translate(gmap, gaddr);
> +		if (IS_ERR_VALUE(vmaddr))
> +			return vmaddr;
> +		pmdp = gmap_pmd_op_walk(gmap, gaddr, vmaddr, &ptl_pmd);
> +		if (pmdp && !(pmd_val(*pmdp) & _SEGMENT_ENTRY_INVALID)) {
> +			if (!pmd_large(*pmdp)) {
> +				ptep = gmap_pte_from_pmd(gmap, pmdp, vmaddr, &ptl_pte);
> +				if (ptep) {
> +					pte = *ptep;
> +					if (pte_present(pte) && (pte_val(pte) & _PAGE_READ)) {
> +						address = pte_val(pte) & PAGE_MASK;
> +						address += gaddr & ~PAGE_MASK;
> +						*val = *(unsigned long *) address;
> +						pte_val(*ptep) |= _PAGE_YOUNG;
> +						/* Do *NOT* clear the _PAGE_INVALID bit! */
> +						rc = 0;
> +					}
> +				}
> +				gmap_pte_op_end(ptl_pte);

I'm confused that we have a gmap_pte_op_end() followed by a
gmap_pmd_op_end() although we never started a gmap_pte_op_walk() ... I
assume this is due to gmap_pte_from_pmd() ? We should find better names
for these functions otherwise this is pure magic.

e.g. gmap_pte_op_walk_pmd() instead of gmap_pte_from_pmd()

... and shouldn't "gmap_pte_op_end(ptl_pte)" be inside of the "if(ptep)" ?

> +			} else {
> +				address = pmd_val(*pmdp) & HPAGE_MASK;
> +				address += gaddr & ~HPAGE_MASK;
>  				*val = *(unsigned long *) address;
> -				pte_val(*ptep) |= _PAGE_YOUNG;
> -				/* Do *NOT* clear the _PAGE_INVALID bit! */
>  				rc = 0;
>  			}
> -			gmap_pte_op_end(ptl);
> +			gmap_pmd_op_end(ptl_pmd);
>  		}
>  		if (!rc)
>  			break;
> -		vmaddr = __gmap_translate(gmap, gaddr);
> -		if (IS_ERR_VALUE(vmaddr)) {
> -			rc = vmaddr;
> -			break;
> -		}
>  		rc = gmap_fixup(gmap, gaddr, vmaddr, PROT_READ);
>  		if (rc)
>  			break;
> 


-- 

Thanks,

David / dhildenb



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