Re: [PATCH v5 06/14] KVM: s390: pv: properly handle page flags for protected guests

Janosch Frank <frankja@xxxxxxxxxxxxx> · Tue, 12 Oct 2021 09:59:50 +0200

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@xxxxxxxxxxxxx>
Acked-by: Janosch Frank <frankja@xxxxxxxxxxxxx>

You can make this one a Reviewed-by

Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
  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;
  }
  








