[v2,2/3] x86/shadow: mark more of sh_page_fault() HVM-only

Commit Message

Jan Beulich Jan. 23, 2023, 2:27 p.m. UTC

The types p2m_is_readonly() checks for aren't applicable to PV;
specifically get_gfn() won't ever return any such type for PV domains.
Extend the HVM-conditional block of code, also past the subsequent HVM-
only if(). This way the "emulate_readonly" also becomes unreachable when
!HVM, so move the conditional there upwards as well. Noticing the
earlier shadow_mode_refcounts() check, move it up even further, right
after that check. With that, the "done" label also needs marking as
potentially unused.

Signed-off-by: Jan Beulich <[e-mail]>
---
v2: Parts split off to a subsequent patch.

Comments

Andrew Cooper Feb. 24, 2023, 4:39 p.m. UTC | #1

On 23/01/2023 2:27 pm, Jan Beulich wrote:
> The types p2m_is_readonly() checks for aren't applicable to PV;
> specifically get_gfn() won't ever return any such type for PV domains.
> Extend the HVM-conditional block of code, also past the subsequent HVM-
> only if(). This way the "emulate_readonly" also becomes unreachable when
> !HVM, so move the conditional there upwards as well. Noticing the
> earlier shadow_mode_refcounts() check, move it up even further, right
> after that check. With that, the "done" label also needs marking as
> potentially unused.
>
> Signed-off-by: Jan Beulich <[e-mail]>

Acked-by: Andrew Cooper <[e-mail]>

Patch

--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -2613,8 +2613,6 @@  static int cf_check sh_page_fault(
                ? EXCRET_fault_fixed : 0;
     }
 
-#endif /* CONFIG_HVM */
-
     /* Ignore attempts to write to read-only memory. */
     if ( p2m_is_readonly(p2mt) && (ft == ft_demand_write) )
         goto emulate_readonly; /* skip over the instruction */
@@ -2633,12 +2631,14 @@  static int cf_check sh_page_fault(
         goto emulate;
     }
 
+#endif /* CONFIG_HVM */
+
     perfc_incr(shadow_fault_fixed);
     d->arch.paging.log_dirty.fault_count++;
     sh_reset_early_unshadow(v);
 
     trace_shadow_fixup(gw.l1e, va);
- done:
+ done: __maybe_unused;
     sh_audit_gw(v, &gw);
     SHADOW_PRINTK("fixed\n");
     shadow_audit_tables(v);
@@ -2650,6 +2650,7 @@  static int cf_check sh_page_fault(
     if ( !shadow_mode_refcounts(d) || !guest_mode(regs) )
         goto not_a_shadow_fault;
 
+#ifdef CONFIG_HVM
     /*
      * We do not emulate user writes. Instead we use them as a hint that the
      * page is no longer a page table. This behaviour differs from native, but
@@ -2677,7 +2678,6 @@  static int cf_check sh_page_fault(
         goto not_a_shadow_fault;
     }
 
-#ifdef CONFIG_HVM
     /* Unshadow if we are writing to a toplevel pagetable that is
      * flagged as a dying process, and that is not currently used. */
     if ( sh_mfn_is_a_page_table(gmfn) && is_hvm_domain(d) &&