[Xen-changelog] [xen master] pvh: Fix regression due to assumption that HVM paths MUST use io-backend device

[patchbot@xxxxxxx]

commit 4e8d89bc1445f91c4c6c7bf0ad8d51b0c809841e
Author:     Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
AuthorDate: Thu Feb 13 17:56:39 2014 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 13 17:56:39 2014 +0100

    pvh: Fix regression due to assumption that HVM paths MUST use io-backend 
device
    
    The commit 09bb434748af9bfe3f7fca4b6eef721a7d5042a4
    "Nested VMX: prohibit virtual vmentry/vmexit during IO emulation"
    assumes that the HVM paths are only taken by HVM guests. With the PVH
    enabled that is no longer the case - which means that we do not have
    to have the IO-backend device (QEMU) enabled.
    
    As such, that patch can crash the hypervisor:
    
    Xen call trace:
        [<ffff82d0801ddd9a>] nvmx_switch_guest+0x4d/0x903
        [<ffff82d0801de95b>] vmx_asm_vmexit_handler+0x4b/0xc0
    
    Pagetable walk from 000000000000001e:
      L4[0x000] = 0000000000000000 ffffffffffffffff
    
    ****************************************
    Panic on CPU 7:
    FATAL PAGE FAULT
    [error_code=0000]
    Faulting linear address: 000000000000001e
    ****************************************
    
    as we do not have an io based backend. In the case that the
    PVH guest does run an HVM guest inside it - we need to do
    further work to suport this - and for now the check will
    bail us out.
    
    We also fix spelling mistakes and the sentence structure.
    
    Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
    Acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
    Release-acked-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
    Acked-by: "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vvmx.c |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c
index d2ba435..40167d6 100644
--- a/xen/arch/x86/hvm/vmx/vvmx.c
+++ b/xen/arch/x86/hvm/vmx/vvmx.c
@@ -1394,13 +1394,17 @@ void nvmx_switch_guest(void)
     struct vcpu *v = current;
     struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v);
     struct cpu_user_regs *regs = guest_cpu_user_regs();
+    const ioreq_t *ioreq = get_ioreq(v);
 
     /*
-     * a pending IO emualtion may still no finished. In this case,
-     * no virtual vmswith is allowed. Or else, the following IO
-     * emulation will handled in a wrong VCPU context.
+     * A pending IO emulation may still be not finished. In this case, no
+     * virtual vmswitch is allowed. Or else, the following IO emulation will
+     * be handled in a wrong VCPU context. If there are no IO backends - PVH
+     * guest by itself or a PVH guest with an HVM guest running inside - we
+     * don't want to continue as this setup is not implemented nor supported
+     * as of right now.
      */
-    if ( get_ioreq(v)->state != STATE_IOREQ_NONE )
+    if ( !ioreq || ioreq->state != STATE_IOREQ_NONE )
         return;
     /*
      * a softirq may interrupt us between a virtual vmentry is
--
generated by git-patchbot for /home/xen/git/xen.git#master

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