Re: [PATCH v2 1/2] KVM: x86: Check hypercall's exit to userspace generically

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On 8/14/2024 7:16 AM, Huang, Kai wrote:


On 13/08/2024 5:12 pm, Binbin Wu wrote:
Check whether a KVM hypercall needs to exit to userspace or not based on
hypercall_exit_enabled field of struct kvm_arch.

Userspace can request a hypercall to exit to userspace for handling by
enable KVM_CAP_EXIT_HYPERCALL and the enabled hypercall will be set in
hypercall_exit_enabled.  Make the check code generic based on it.

Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>

Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>

One nitpicking below:

---
  arch/x86/kvm/x86.c | 4 ++--
  arch/x86/kvm/x86.h | 7 +++++++
  2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index af6c8cf6a37a..6e16c9751af7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10226,8 +10226,8 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
      cpl = kvm_x86_call(get_cpl)(vcpu);
        ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl);
-    if (nr == KVM_HC_MAP_GPA_RANGE && !ret)
-        /* MAP_GPA tosses the request to the user space. */
+    if (!ret && is_kvm_hc_exit_enabled(vcpu->kvm, nr))
+        /* The hypercall is requested to exit to userspace. */
          return 0;

I believe you put "!ret" check first for a reason?  Perhaps you can add a comment.


Yes, check "!ret" first to make sure the input of is_kvm_hc_exit_enabled() is a valid KVM_HC_*.
Will add a comment.
Thanks.





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