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Date: Tue, 7 May 2024 18:25:15 +0200
From: Claudio Imbrenda <imbrenda@linux.ibm.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
        Vasily
 Gorbik <gor@linux.ibm.com>,
        Alexander Gordeev <agordeev@linux.ibm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Sven Schnelle
 <svens@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Gerald
 Schaefer <gerald.schaefer@linux.ibm.com>,
        Matthew Wilcox
 <willy@infradead.org>, Thomas Huth <thuth@redhat.com>
Subject: Re: [PATCH v2 07/10] s390/uv: convert uv_destroy_owned_page() to
 uv_destroy_(folio|pte)()
Message-ID: <20240507182515.0ce19da5@p-imbrenda.boeblingen.de.ibm.com>
In-Reply-To: <20240412142120.220087-8-david@redhat.com>
References: <20240412142120.220087-1-david@redhat.com>
	<20240412142120.220087-8-david@redhat.com>
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On Fri, 12 Apr 2024 16:21:17 +0200
David Hildenbrand <david@redhat.com> wrote:

> Let's have the following variants for destroying pages:
> 
> (1) uv_destroy(): Like uv_pin_shared() and uv_convert_from_secure(),
> "low level" helper that operates on paddr and doesn't mess with folios.
> 
> (2) uv_destroy_folio(): Consumes a folio to which we hold a reference.
> 
> (3) uv_destroy_pte(): Consumes a PTE that holds a reference through the
> mapping.
> 
> Unfortunately we need uv_destroy_pte(), because pfn_folio() and
> friends are not available in pgtable.h.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
>  arch/s390/include/asm/pgtable.h |  2 +-
>  arch/s390/include/asm/uv.h      | 10 ++++++++--
>  arch/s390/kernel/uv.c           | 24 +++++++++++++++++-------
>  arch/s390/mm/gmap.c             |  6 ++++--
>  4 files changed, 30 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index 60950e7a25f5..97e040617c29 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -1199,7 +1199,7 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
>  	 * The notifier should have destroyed all protected vCPUs at this
>  	 * point, so the destroy should be successful.
>  	 */
> -	if (full && !uv_destroy_owned_page(pte_val(res) & PAGE_MASK))
> +	if (full && !uv_destroy_pte(res))
>  		return res;
>  	/*
>  	 * If something went wrong and the page could not be destroyed, or
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index d2205ff97007..a1bef30066ef 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -483,7 +483,8 @@ static inline int is_prot_virt_host(void)
>  int uv_pin_shared(unsigned long paddr);
>  int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb);
>  int gmap_destroy_page(struct gmap *gmap, unsigned long gaddr);
> -int uv_destroy_owned_page(unsigned long paddr);
> +int uv_destroy_folio(struct folio *folio);
> +int uv_destroy_pte(pte_t pte);
>  int uv_convert_owned_from_secure(unsigned long paddr);
>  int gmap_convert_to_secure(struct gmap *gmap, unsigned long gaddr);
>  
> @@ -497,7 +498,12 @@ static inline int uv_pin_shared(unsigned long paddr)
>  	return 0;
>  }
>  
> -static inline int uv_destroy_owned_page(unsigned long paddr)
> +static inline int uv_destroy_folio(struct folio *folio)
> +{
> +	return 0;
> +}
> +
> +static inline int uv_destroy_pte(pte_t pte)
>  {
>  	return 0;
>  }
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index 3d3250b406a6..61c1ce51c883 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -110,7 +110,7 @@ EXPORT_SYMBOL_GPL(uv_pin_shared);
>   *
>   * @paddr: Absolute host address of page to be destroyed
>   */
> -static int uv_destroy_page(unsigned long paddr)
> +static int uv_destroy(unsigned long paddr)
>  {
>  	struct uv_cb_cfs uvcb = {
>  		.header.cmd = UVC_CMD_DESTR_SEC_STOR,
> @@ -131,11 +131,10 @@ static int uv_destroy_page(unsigned long paddr)
>  }
>  
>  /*
> - * The caller must already hold a reference to the page
> + * The caller must already hold a reference to the folio
>   */
> -int uv_destroy_owned_page(unsigned long paddr)
> +int uv_destroy_folio(struct folio *folio)
>  {
> -	struct folio *folio = phys_to_folio(paddr);
>  	int rc;
>  
>  	/* See gmap_make_secure(): large folios cannot be secure */
> @@ -143,13 +142,22 @@ int uv_destroy_owned_page(unsigned long paddr)
>  		return 0;
>  
>  	folio_get(folio);
> -	rc = uv_destroy_page(paddr);
> +	rc = uv_destroy(folio_to_phys(folio));
>  	if (!rc)
>  		clear_bit(PG_arch_1, &folio->flags);
>  	folio_put(folio);
>  	return rc;
>  }
>  
> +/*
> + * The present PTE still indirectly holds a folio reference through the mapping.
> + */
> +int uv_destroy_pte(pte_t pte)
> +{
> +	VM_WARN_ON(!pte_present(pte));
> +	return uv_destroy_folio(pfn_folio(pte_pfn(pte)));
> +}
> +
>  /*
>   * Requests the Ultravisor to encrypt a guest page and make it
>   * accessible to the host for paging (export).
> @@ -437,6 +445,7 @@ int gmap_destroy_page(struct gmap *gmap, unsigned long gaddr)
>  {
>  	struct vm_area_struct *vma;
>  	unsigned long uaddr;
> +	struct folio *folio;
>  	struct page *page;
>  	int rc;
>  
> @@ -460,7 +469,8 @@ int gmap_destroy_page(struct gmap *gmap, unsigned long gaddr)
>  	page = follow_page(vma, uaddr, FOLL_WRITE | FOLL_GET);
>  	if (IS_ERR_OR_NULL(page))
>  		goto out;
> -	rc = uv_destroy_owned_page(page_to_phys(page));
> +	folio = page_folio(page);
> +	rc = uv_destroy_folio(folio);
>  	/*
>  	 * Fault handlers can race; it is possible that two CPUs will fault
>  	 * on the same secure page. One CPU can destroy the page, reboot,
> @@ -472,7 +482,7 @@ int gmap_destroy_page(struct gmap *gmap, unsigned long gaddr)
>  	 */
>  	if (rc)
>  		rc = uv_convert_owned_from_secure(page_to_phys(page));
> -	put_page(page);
> +	folio_put(folio);
>  out:
>  	mmap_read_unlock(gmap->mm);
>  	return rc;
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 094b43b121cd..0351cb139df4 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2756,13 +2756,15 @@ static const struct mm_walk_ops gather_pages_ops = {
>   */
>  void s390_uv_destroy_pfns(unsigned long count, unsigned long *pfns)
>  {
> +	struct folio *folio;
>  	unsigned long i;
>  
>  	for (i = 0; i < count; i++) {
> +		folio = pfn_folio(pfns[i]);
>  		/* we always have an extra reference */
> -		uv_destroy_owned_page(pfn_to_phys(pfns[i]));
> +		uv_destroy_folio(folio);
>  		/* get rid of the extra reference */
> -		put_page(pfn_to_page(pfns[i]));
> +		folio_put(folio);
>  		cond_resched();
>  	}
>  }