KVM: x86: Always complete hypercall via function callback

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Finish "emulation" of KVM hypercalls by function callback, even when the
hypercall is handled entirely within KVM, i.e. doesn't require an exit to
userspace, and refactor __kvm_emulate_hypercall()'s return value to *only*
communicate whether or not KVM should exit to userspace or resume the
guest.

(Ab)Use vcpu->run->hypercall.ret to propagate the return value to the
callback, purely to avoid having to add a trampoline for every completion
callback.

Using the function return value for KVM's control flow eliminates the
multiplexed return value, where '0' for KVM_HC_MAP_GPA_RANGE (and only
that hypercall) means "exit to userspace".

Note, the unnecessary extra indirect call and thus potential retpoline
will be eliminated in the near future by converting the intermediate layer
to a macro.

Suggested-by: Binbin Wu <binbin.wu@linux.intel.com>
Suggested-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20241128004344.4072099-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Sean Christopherson 2024-11-27 16:43:43 -08:00 • committed by Paolo Bonzini

parent 05a518b49d

commit d9eb86a6f4

2 changed files with 17 additions and 21 deletions

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28

arch/x86/kvm/x86.c

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10

arch/x86/kvm/x86.h

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