[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH 17/17] xen: Switch parameter in get_page_from_gfn to use typesafe gfn

Hi Jan,

On 27/03/2020 13:50, Jan Beulich wrote:
On 22.03.2020 17:14, julien@xxxxxxx wrote:
--- a/xen/arch/x86/hvm/domain.c
+++ b/xen/arch/x86/hvm/domain.c
@@ -296,8 +296,10 @@ int arch_set_info_hvm_guest(struct vcpu *v, const 
vcpu_hvm_context_t *ctx)
      if ( hvm_paging_enabled(v) && !paging_mode_hap(v->domain) )
          /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
-        struct page_info *page = get_page_from_gfn(v->domain,
-                                 v->arch.hvm.guest_cr[3] >> PAGE_SHIFT,
+        struct page_info *page;
+        page = get_page_from_gfn(v->domain,
+                                 gaddr_to_gfn(v->arch.hvm.guest_cr[3]),

My earlier comment on this remains - I thing this conversion makes
the problem this expression has more hidden than with the shift.
This would better use a gfn_from_cr3() helper (or whatever it'll
be that it gets named). Same elsewhere in this patch then.

I will have a closer look the *cr3 helpers and reply with some suggestions.

@@ -2363,7 +2364,7 @@ int hvm_set_cr3(unsigned long value, bool may_defer)
          /* Shadow-mode CR3 change. Check PDBR and update refcounts. */
          HVM_DBG_LOG(DBG_LEVEL_VMMU, "CR3 value = %lx", value);
-        page = get_page_from_gfn(v->domain, value >> PAGE_SHIFT,
+        page = get_page_from_gfn(v->domain, cr3_to_gfn(value),

Oh, seeing this I recall Paul did point out the above already.

@@ -508,7 +508,7 @@ int evtchn_fifo_init_control(struct evtchn_init_control 
      struct domain *d = current->domain;
      uint32_t vcpu_id;
-    uint64_t gfn;
+    gfn_t gfn;
      uint32_t offset;
      struct vcpu *v;
      int rc;
@@ -516,7 +516,7 @@ int evtchn_fifo_init_control(struct evtchn_init_control 
      init_control->link_bits = EVTCHN_FIFO_LINK_BITS;
vcpu_id = init_control->vcpu;
-    gfn     = init_control->control_gfn;
+    gfn     = _gfn(init_control->control_gfn);

There's silent truncation here now for Arm32, afaict. Are we really
okay with this?

Well, the truncation was already silently happening as we call get_page_from_gfn() in map_guest_page(). So it is not worse than the current situation.

Although, there are a slight advantage with the new code as you can more easily spot potential truncation. Indeed, you could add some type check in _gfn().


Julien Grall



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.