[Xen-devel] [PATCH] Allow VCPUOP_register_vcpu_info to work again on PVHVM guests.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

For details on the hypercall please see commit
c58ae69360ccf2495a19bf4ca107e21cf873c75b (VCPUOP_register_vcpu_info) and
the c/s 23143 (git commit 6b063a4a6f44245a727aa04ef76408b2e00af9c7)
(x86: move pv-only members of struct vcpu to struct pv_vcpu)
that introduced the regression.

The current code allows the PVHVM guest to make this hypercall.
But for PVHVM guest it always returns -EINVAL (-22) for Xen 4.2
and above. Xen 4.1 and earlier worked.

The reason is that the check in map_vcpu_info would fail
at:

  if ( v->arch.vcpu_info_mfn != INVALID_MFN )

The reason is that the vcpu_info_mfn for PVHVM guests ends up by
defualt with the value of zero (introduced by c/s 23143).

The code in vcpu_initialise which initialized vcpu_info_mfn to a
valid value (INVALID_MFN), would never be called for PVHVM:

    if ( is_hvm_domain(d) )
    {
        rc = hvm_vcpu_initialise(v);
        goto done;
    }

    v->arch.pv_vcpu.vcpu_info_mfn = INVALID_MFN;

while previously it would be:

     v->arch.vcpu_info_mfn = INVALID_MFN;

[right at the start of the function in Xen 4.1]

This fixes the problem with Linux advertising this error:
register_vcpu_info failed: err=-22

CC: jbeulich@xxxxxxxx
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 xen/arch/x86/domain.c        | 13 +++++++------
 xen/include/asm-x86/domain.h |  6 +++---
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 6f9cbed..14b6d13 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -387,13 +387,14 @@ int vcpu_initialise(struct vcpu *v)
 
     vmce_init_vcpu(v);
 
+    v->arch.vcpu_info_mfn = INVALID_MFN;
+
     if ( is_hvm_domain(d) )
     {
         rc = hvm_vcpu_initialise(v);
         goto done;
     }
 
-    v->arch.pv_vcpu.vcpu_info_mfn = INVALID_MFN;
 
     spin_lock_init(&v->arch.pv_vcpu.shadow_ldt_lock);
 
@@ -963,14 +964,14 @@ unmap_vcpu_info(struct vcpu *v)
 {
     unsigned long mfn;
 
-    if ( v->arch.pv_vcpu.vcpu_info_mfn == INVALID_MFN )
+    if ( v->arch.vcpu_info_mfn == INVALID_MFN )
         return;
 
-    mfn = v->arch.pv_vcpu.vcpu_info_mfn;
+    mfn = v->arch.vcpu_info_mfn;
     unmap_domain_page_global(v->vcpu_info);
 
     v->vcpu_info = &dummy_vcpu_info;
-    v->arch.pv_vcpu.vcpu_info_mfn = INVALID_MFN;
+    v->arch.vcpu_info_mfn = INVALID_MFN;
 
     put_page_and_type(mfn_to_page(mfn));
 }
@@ -993,7 +994,7 @@ map_vcpu_info(struct vcpu *v, unsigned long gfn, unsigned 
offset)
     if ( offset > (PAGE_SIZE - sizeof(vcpu_info_t)) )
         return -EINVAL;
 
-    if ( v->arch.pv_vcpu.vcpu_info_mfn != INVALID_MFN )
+    if ( v->arch.vcpu_info_mfn != INVALID_MFN )
         return -EINVAL;
 
     /* Run this command on yourself or on other offline VCPUS. */
@@ -1030,7 +1031,7 @@ map_vcpu_info(struct vcpu *v, unsigned long gfn, unsigned 
offset)
     }
 
     v->vcpu_info = new_info;
-    v->arch.pv_vcpu.vcpu_info_mfn = page_to_mfn(page);
+    v->arch.vcpu_info_mfn = page_to_mfn(page);
 
     /* Set new vcpu_info pointer /before/ setting pending flags. */
     wmb();
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 6f9744a..43b4d3d 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -374,9 +374,6 @@ struct pv_vcpu
     /* Current LDT details. */
     unsigned long shadow_ldt_mapcnt;
     spinlock_t shadow_ldt_lock;
-
-    /* Guest-specified relocation of vcpu_info. */
-    unsigned long vcpu_info_mfn;
 };
 
 struct arch_vcpu
@@ -442,6 +439,9 @@ struct arch_vcpu
 
     /* A secondary copy of the vcpu time info. */
     XEN_GUEST_HANDLE(vcpu_time_info_t) time_info_guest;
+
+    /* Guest-specified relocation of vcpu_info. */
+    unsigned long vcpu_info_mfn;
 } __cacheline_aligned;
 
 /* Shorthands to improve code legibility. */
-- 
1.8.1.4


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