[Xen-devel] [PATCH RFC 1/2] xen/pvh: take the p2m lock when doing logdirty ops from HVM domains

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Due to locking order, the p2m lock must be taken before the paging lock, or
else the following panic occurs when trying to use logdirty ops from a PVH
Dom0:

(XEN) mm locking order violation: 292 > 222
(XEN) Xen BUG at mm-locks.h:140
(XEN) ----[ Xen-4.5-unstable  x86_64  debug=y  Not tainted ]----
(XEN) CPU:    1
(XEN) RIP:    e008:[<ffff82d0801e9ea5>] get_page_from_gfn_p2m+0xb0/0x286
(XEN) RFLAGS: 0000000000010282   CONTEXT: hypervisor
(XEN) rax: 0000000000000000   rbx: ffff83019a1f7884   rcx: 0000000000000000
(XEN) rdx: ffff83019a1f0000   rsi: 000000000000000a   rdi: ffff82d0802926c0
(XEN) rbp: ffff83019a1f77f8   rsp: ffff83019a1f7798   r8:  ffff83019e830000
(XEN) r9:  0000000000000003   r10: 00000000000000de   r11: 0000000000000003
(XEN) r12: ffff83019a1f77c4   r13: ffff83019a138820   r14: ffff83019a1f7974
(XEN) r15: 0000000000057431   cr0: 0000000080050033   cr4: 00000000000026f0
(XEN) cr3: 000000019ea86000   cr2: 000000080205d000
(XEN) ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: 0000   cs: e008
[...]
(XEN) Xen call trace:
(XEN)    [<ffff82d0801e9ea5>] get_page_from_gfn_p2m+0xb0/0x286
(XEN)    [<ffff82d0802223e9>] hap_p2m_ga_to_gfn_4_levels+0x59/0x2b7
(XEN)    [<ffff82d080222663>] hap_gva_to_gfn_4_levels+0x1c/0x29
(XEN)    [<ffff82d0801edf67>] paging_gva_to_gfn+0xb8/0xce
(XEN)    [<ffff82d0801b9bc0>] clear_user_hvm+0xd7/0x324
(XEN)    [<ffff82d0801e8776>] paging_log_dirty_op+0x358/0x552
(XEN)    [<ffff82d0801e8d47>] paging_domctl+0x140/0x177
(XEN)    [<ffff82d08015ccca>] arch_do_domctl+0x212/0x269e
(XEN)    [<ffff82d08010487c>] do_domctl+0x195d/0x1cd1
(XEN)    [<ffff82d0801bafba>] hvm_do_hypercall+0x1b8/0x31c
(XEN)    [<ffff82d0801e0d3f>] vmx_vmexit_handler+0xf91/0x1a5f
(XEN)    [<ffff82d0801e7a51>] vmx_asm_vmexit_handler+0x41/0xc0
(XEN)
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 1:
(XEN) Xen BUG at mm-locks.h:140
(XEN) ****************************************
(XEN)
(XEN) Reboot in five seconds...

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/mm/paging.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index 6b788f7..5af6309 100644
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -412,6 +412,8 @@ static int paging_log_dirty_op(struct domain *d,
 
     if ( !resuming )
         domain_pause(d);
+     if (has_hvm_container_vcpu(current))
+         p2m_lock(p2m_get_hostp2m(current->domain));
     paging_lock(d);
 
     if ( !d->arch.paging.preempt.dom )
@@ -421,6 +423,8 @@ static int paging_log_dirty_op(struct domain *d,
               d->arch.paging.preempt.op != sc->op )
     {
         paging_unlock(d);
+        if (has_hvm_container_vcpu(current))
+            p2m_unlock(p2m_get_hostp2m(current->domain));
         ASSERT(!resuming);
         domain_unpause(d);
         return -EBUSY;
@@ -533,6 +537,8 @@ static int paging_log_dirty_op(struct domain *d,
     }
 
     paging_unlock(d);
+    if (has_hvm_container_vcpu(current))
+        p2m_unlock(p2m_get_hostp2m(current->domain));
 
     if ( rv )
     {
@@ -555,6 +561,8 @@ static int paging_log_dirty_op(struct domain *d,
  out:
     d->arch.paging.preempt.dom = NULL;
     paging_unlock(d);
+    if (has_hvm_container_vcpu(current))
+        p2m_unlock(p2m_get_hostp2m(current->domain));
     domain_unpause(d);
 
     if ( l1 )
-- 
1.9.3 (Apple Git-50)


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