linux-kernel - Re: [PATCH v2 03/13] KVM: s390: pv: properly handle page flags for protected guests

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Message-ID: <825b1d54-39ea-334d-e637-a26995780f53@linux.ibm.com>
Date:   Thu, 29 Jul 2021 13:43:25 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     cohuck@...hat.com, borntraeger@...ibm.com, thuth@...hat.com,
        pasic@...ux.ibm.com, david@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/13] KVM: s390: pv: properly handle page flags for
 protected guests

On 7/28/21 4:26 PM, 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@...ux.ibm.com>

Acked-by: Janosch Frank <frankja@...ux.ibm.com>

> ---
>  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 12c5f006c136..bbd51aa94d05 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -351,8 +351,9 @@ 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);
> @@ -362,7 +363,7 @@ 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;
>  }
> @@ -371,6 +372,11 @@ 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 fd0faa51c1bb..5a6ac965f379 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 9bb2c7512cd5..de679facc720 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;
>  }
>  
>