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Re: [PATCH v3 10/10] arm64: Change type of hsr, cpsr, spsr_el1 to uint64_t


On 11/05/2021 07:37, Michal Orzel wrote:
On 05.05.2021 10:00, Jan Beulich wrote:
On 05.05.2021 09:43, Michal Orzel wrote:
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -267,10 +267,10 @@ struct vcpu_guest_core_regs
/* Return address and mode */
      __DECL_REG(pc64,         pc32);             /* ELR_EL2 */
-    uint32_t cpsr;                              /* SPSR_EL2 */
+    uint64_t cpsr;                              /* SPSR_EL2 */
union {
-        uint32_t spsr_el1;       /* AArch64 */
+        uint64_t spsr_el1;       /* AArch64 */
          uint32_t spsr_svc;       /* AArch32 */

This change affects, besides domctl, also default_initialise_vcpu(),
which Arm's arch_initialise_vcpu() calls. I realize do_arm_vcpu_op()
only allows two unrelated VCPUOP_* to pass, but then I don't
understand why arch_initialise_vcpu() doesn't simply return e.g.
-EOPNOTSUPP. Hence I suspect I'm missing something.

I think it is just an overlooked when reviewing the following commit:

commit 192df6f9122ddebc21d0a632c10da3453aeee1c2
Author: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Date:   Tue Dec 15 14:12:32 2015 +0100

    x86: allow HVM guests to use hypercalls to bring up vCPUs

    Allow the usage of the VCPUOP_initialise, VCPUOP_up, VCPUOP_down,
    VCPUOP_is_up, VCPUOP_get_physid and VCPUOP_send_nmi hypercalls from HVM

This patch introduces a new structure (vcpu_hvm_context) that should be used in conjuction with the VCPUOP_initialise hypercall in order to initialize
    vCPUs for HVM guests.

    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

On Arm, the structure vcpu_guest_context is not exposed outside of Xen and the tools. Interestingly vcpu_guest_core_regs is but it should only be used within vcpu_guest_context.

So as this is not used by stable ABI, it is fine to break it.

I agree that do_arm_vcpu_op only allows two VCPUOP* to pass and
arch_initialise_vcpu being called in case of VCPUOP_initialise
has no sense as VCPUOP_initialise is not supported on arm.
It makes sense that it should return -EOPNOTSUPP.
However do_arm_vcpu_op will not accept VCPUOP_initialise and will return
-EINVAL. So arch_initialise_vcpu for arm will not be called.
Do you think that changing this behaviour so that arch_initialise_vcpu returns
-EOPNOTSUPP should be part of this patch?

I think this change is unrelated. So it should be handled in a follow-up patch.

If you are taking care of this, would you mind to also look to move struct vcpu_guest_core_regs within the #if defined(__XEN__) || defined(__XEN_TOOLS__)?

I will attempt to do a proper review of this patch by the end of the week.


Julien Grall



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