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Date: Tue, 12 Oct 2021 09:59:50 +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, Ulrich.Weigand@...ibm.com
Subject: Re: [PATCH v5 06/14] KVM: s390: pv: properly handle page flags for
protected guests
On 9/20/21 15:24, 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.
>
> The PG_arch_1 flag is always allowed to overindicate; using the new
> functions introduced here allows to reduce the extent of overindication
> and thus improve performance.
>
> 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>
You can make this one a Reviewed-by
> Reviewed-by: Christian Borntraeger <borntraeger@...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 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;
> }
>
>
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