[Xen-changelog] [xen master] x86/ioreq server: release the p2m lock after mmio is handled

[patchbot@xxxxxxx]

commit d909cb99998cd63761e238c59e274450c7dacd8e
Author:     Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
AuthorDate: Fri Apr 7 17:35:44 2017 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Apr 7 17:35:44 2017 +0200

    x86/ioreq server: release the p2m lock after mmio is handled
    
    Routine hvmemul_do_io() may need to peek the p2m type of a gfn to
    select the ioreq server. For example, operations on gfns with
    p2m_ioreq_server type will be delivered to a corresponding ioreq
    server, and this requires that the p2m type not be switched back
    to p2m_ram_rw during the emulation process. To avoid this race
    condition, we delay the release of p2m lock in hvm_hap_nested_page_fault()
    until mmio is handled.
    
    Note: previously in hvm_hap_nested_page_fault(), put_gfn() was moved
    before the handling of mmio, due to a deadlock risk between the p2m
    lock and the event lock(in commit 77b8dfe). Later, a per-event channel
    lock was introduced in commit de6acb7, to send events. So we do not
    need to worry about the deadlock issue.
    
    Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 35531ae..f50d15f 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1843,15 +1843,10 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned 
long gla,
          (npfec.write_access &&
           (p2m_is_discard_write(p2mt) || (p2mt == p2m_ioreq_server))) )
     {
-        __put_gfn(p2m, gfn);
-        if ( ap2m_active )
-            __put_gfn(hostp2m, gfn);
-
-        rc = 0;
         if ( !handle_mmio_with_translation(gla, gpa >> PAGE_SHIFT, npfec) )
             hvm_inject_hw_exception(TRAP_gp_fault, 0);
         rc = 1;
-        goto out;
+        goto out_put_gfn;
     }
 
     /* Check if the page has been paged out */
--
generated by git-patchbot for /home/xen/git/xen.git#master

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