Re: [PATCH v4 06/14] KVM: s390: pv: properly handle page flags for protected guests

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 18.08.21 15:26, Claudio Imbrenda wrote:
> Introduce variants of the convert and destroy page functions that also
> clear the PG_arch_1 bit used to mark them as secure pages.
> 
> These new functions can only be called on pages for which a reference
> is already being held.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Acked-by: Janosch Frank <frankja@linux.ibm.com>

Can you refresh my mind? We do have over-indication of PG_arch_1 and this
might result in spending some unneeded cycles but in the end this will be
correct. Right?
And this patch will fix some unnecessary places that add overindication.
> ---
>   arch/s390/include/asm/pgtable.h |  9 ++++++---
>   arch/s390/include/asm/uv.h      | 10 ++++++++--
>   arch/s390/kernel/uv.c           | 34 ++++++++++++++++++++++++++++++++-
>   arch/s390/mm/gmap.c             |  4 +++-
>   4 files changed, 50 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index dcac7b2df72c..0f1af2232ebe 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -1074,8 +1074,9 @@ static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
>   	pte_t res;
>   
>   	res = ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
> +	/* At this point the reference through the mapping is still present */
>   	if (mm_is_protected(mm) && pte_present(res))
> -		uv_convert_from_secure(pte_val(res) & PAGE_MASK);
> +		uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
>   	return res;
>   }
>   
> @@ -1091,8 +1092,9 @@ static inline pte_t ptep_clear_flush(struct vm_area_struct *vma,
>   	pte_t res;
>   
>   	res = ptep_xchg_direct(vma->vm_mm, addr, ptep, __pte(_PAGE_INVALID));
> +	/* At this point the reference through the mapping is still present */
>   	if (mm_is_protected(vma->vm_mm) && pte_present(res))
> -		uv_convert_from_secure(pte_val(res) & PAGE_MASK);
> +		uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
>   	return res;
>   }
>   
> @@ -1116,8 +1118,9 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
>   	} else {
>   		res = ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
>   	}
> +	/* At this point the reference through the mapping is still present */
>   	if (mm_is_protected(mm) && pte_present(res))
> -		uv_convert_from_secure(pte_val(res) & PAGE_MASK);
> +		uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
>   	return res;
>   }
>   
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index b35add51b967..3236293d5a31 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -356,8 +356,9 @@ static inline int is_prot_virt_host(void)
>   }
>   
>   int gmap_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb);
> -int uv_destroy_page(unsigned long paddr);
> +int uv_destroy_owned_page(unsigned long paddr);
>   int uv_convert_from_secure(unsigned long paddr);
> +int uv_convert_owned_from_secure(unsigned long paddr);
>   int gmap_convert_to_secure(struct gmap *gmap, unsigned long gaddr);
>   
>   void setup_uv(void);
> @@ -367,7 +368,7 @@ void adjust_to_uv_max(unsigned long *vmax);
>   static inline void setup_uv(void) {}
>   static inline void adjust_to_uv_max(unsigned long *vmax) {}
>   
> -static inline int uv_destroy_page(unsigned long paddr)
> +static inline int uv_destroy_owned_page(unsigned long paddr)
>   {
>   	return 0;
>   }
> @@ -376,6 +377,11 @@ static inline int uv_convert_from_secure(unsigned long paddr)
>   {
>   	return 0;
>   }
> +
> +static inline int uv_convert_owned_from_secure(unsigned long paddr)
> +{
> +	return 0;
> +}
>   #endif
>   
>   #if defined(CONFIG_PROTECTED_VIRTUALIZATION_GUEST) || IS_ENABLED(CONFIG_KVM)
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index 68a8fbafcb9c..05f8bf61d20a 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -115,7 +115,7 @@ static int uv_pin_shared(unsigned long paddr)
>    *
>    * @paddr: Absolute host address of page to be destroyed
>    */
> -int uv_destroy_page(unsigned long paddr)
> +static int uv_destroy_page(unsigned long paddr)
>   {
>   	struct uv_cb_cfs uvcb = {
>   		.header.cmd = UVC_CMD_DESTR_SEC_STOR,
> @@ -135,6 +135,22 @@ int uv_destroy_page(unsigned long paddr)
>   	return 0;
>   }
>   
> +/*
> + * The caller must already hold a reference to the page
> + */
> +int uv_destroy_owned_page(unsigned long paddr)
> +{
> +	struct page *page = phys_to_page(paddr);
> +	int rc;
> +
> +	get_page(page);
> +	rc = uv_destroy_page(paddr);
> +	if (!rc)
> +		clear_bit(PG_arch_1, &page->flags);
> +	put_page(page);
> +	return rc;
> +}
> +
>   /*
>    * Requests the Ultravisor to encrypt a guest page and make it
>    * accessible to the host for paging (export).
> @@ -154,6 +170,22 @@ int uv_convert_from_secure(unsigned long paddr)
>   	return 0;
>   }
>   
> +/*
> + * The caller must already hold a reference to the page
> + */
> +int uv_convert_owned_from_secure(unsigned long paddr)
> +{
> +	struct page *page = phys_to_page(paddr);
> +	int rc;
> +
> +	get_page(page);
> +	rc = uv_convert_from_secure(paddr);
> +	if (!rc)
> +		clear_bit(PG_arch_1, &page->flags);
> +	put_page(page);
> +	return rc;
> +}
> +
>   /*
>    * Calculate the expected ref_count for a page that would otherwise have no
>    * further pins. This was cribbed from similar functions in other places in
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 5a138f6220c4..38b792ab57f7 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -2678,8 +2678,10 @@ static int __s390_reset_acc(pte_t *ptep, unsigned long addr,
>   {
>   	pte_t pte = READ_ONCE(*ptep);
>   
> +	/* There is a reference through the mapping */
>   	if (pte_present(pte))
> -		WARN_ON_ONCE(uv_destroy_page(pte_val(pte) & PAGE_MASK));
> +		WARN_ON_ONCE(uv_destroy_owned_page(pte_val(pte) & PAGE_MASK));
> +
>   	return 0;
>   }
>   
>