x86/svm: do not try to handle recalc NPT faults immediately

A recalculation NPT fault doesn't always require additional handling
in hvm_hap_nested_page_fault(), moreover in general case if there is no
explicit handling done there - the fault is wrongly considered fatal.

This covers a specific case of migration with vGPU assigned which
uses direct MMIO mappings made by XEN_DOMCTL_memory_mapping hypercall:
at a moment log-dirty is enabled globally, recalculation is requested
for the whole guest memory including those mapped MMIO regions
which causes a page fault being raised at the first access to them;
but due to MMIO P2M type not having any explicit handling in
hvm_hap_nested_page_fault() a domain is erroneously crashed with unhandled
SVM violation.

Instead of trying to be opportunistic - use safer approach and handle
P2M recalculation in a separate NPT fault by attempting to retry after
making the necessary adjustments. This is aligned with Intel behavior
where there are separate VMEXITs for recalculation and EPT violations
(faults) and only faults are handled in hvm_hap_nested_page_fault().
Do it by also unifying do_recalc return code with Intel implementation
where returning 1 means P2M was actually changed.

Since there was no case previously where p2m_pt_handle_deferred_changes()
could return a positive value - it's safe to replace ">= 0" with just "== 0"
in VMEXIT_NPF handler. finish_type_change() is also not affected by the
change as being able to deal with >0 return value of p2m->recalc from
EPT implementation.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Paul Durrant <paul@xen.org>

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 44ff9d0c6b476ed0baa23f14c768ce54bcfaa4aa..4eb41792e2a916dd6038ca2d4afe973c1445a1e4 100644 (file)
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -2923,9 +2923,10 @@ void svm_vmexit_handler(struct cpu_user_regs *regs)
             v->arch.hvm.svm.cached_insn_len = vmcb->guest_ins_len & 0xf;
         rc = vmcb->exitinfo1 & PFEC_page_present
              ? p2m_pt_handle_deferred_changes(vmcb->exitinfo2) : 0;
-        if ( rc >= 0 )
+        if ( rc == 0 )
+            /* If no recal adjustments were being made - handle this fault */
             svm_do_nested_pgfault(v, regs, vmcb->exitinfo1, vmcb->exitinfo2);
-        else
+        else if ( rc < 0 )
         {
             printk(XENLOG_G_ERR
                    "%pv: Error %d handling NPF (gpa=%08lx ec=%04lx)\n",

diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
index 5c0501794ee6e06aa5f5f69a8597e8f1ed306b69..badb26bc34bf9348438760d7ed1c37169eaf8845 100644 (file)
--- a/xen/arch/x86/mm/p2m-pt.c
+++ b/xen/arch/x86/mm/p2m-pt.c
@@ -341,6 +341,7 @@ static int do_recalc(struct p2m_domain *p2m, unsigned long gfn)
     unsigned int level = 4;
     l1_pgentry_t *pent;
     int err = 0;
+    bool recalc_done = false;
 
     table = map_domain_page(pagetable_get_mfn(p2m_get_pagetable(p2m)));
     while ( --level )
@@ -402,6 +403,8 @@ static int do_recalc(struct p2m_domain *p2m, unsigned long gfn)
                 clear_recalc(l1, e);
                 err = p2m->write_p2m_entry(p2m, gfn, pent, e, level + 1);
                 ASSERT(!err);
+
+                recalc_done = true;
             }
         }
         unmap_domain_page((void *)((unsigned long)pent & PAGE_MASK));
@@ -448,12 +451,14 @@ static int do_recalc(struct p2m_domain *p2m, unsigned long gfn)
             clear_recalc(l1, e);
         err = p2m->write_p2m_entry(p2m, gfn, pent, e, level + 1);
         ASSERT(!err);
+
+        recalc_done = true;
     }
 
  out:
     unmap_domain_page(table);
 
-    return err;
+    return err ?: recalc_done;
 }
 
 int p2m_pt_handle_deferred_changes(uint64_t gpa)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 17f320b624ec9569fff449593779966aae57ac8c..db7bde02309cd74edef5c926d9e2e29c5de45da1 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1197,7 +1197,7 @@ static int finish_type_change(struct p2m_domain *p2m,
         rc = p2m->recalc(p2m, gfn);
         /*
          * ept->recalc could return 0/1/-ENOMEM. pt->recalc could return
-         * 0/-ENOMEM/-ENOENT, -ENOENT isn't an error as we are looping
+         * 0/1/-ENOMEM/-ENOENT, -ENOENT isn't an error as we are looping
          * gfn here. If rc is 1 we need to have it 0 for success.
          */
         if ( rc == -ENOENT || rc > 0 )