Re: [PATCH v6 2/7] KVM: VMX: Use is_64_bit_mode() to check 64-bit mode

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On 3/29/2023 10:04 AM, Huang, Kai wrote:
On Wed, 2023-03-29 at 09:27 +0800, Binbin Wu wrote:
On 3/29/2023 7:33 AM, Huang, Kai wrote:
On Tue, 2023-03-21 at 14:35 -0700, Sean Christopherson wrote:
On Mon, Mar 20, 2023, Chao Gao wrote:
On Sun, Mar 19, 2023 at 04:49:22PM +0800, Binbin Wu wrote:
get_vmx_mem_address() and sgx_get_encls_gva() use is_long_mode()
to check 64-bit mode. Should use is_64_bit_mode() instead.

Fixes: f9eb4af67c9d ("KVM: nVMX: VMX instructions: add checks for #GP/#SS exceptions")
Fixes: 70210c044b4e ("KVM: VMX: Add SGX ENCLS[ECREATE] handler to enforce CPUID restrictions")
It is better to split this patch into two: one for nested and one for
SGX.

It is possible that there is a kernel release which has just one of
above two flawed commits, then this fix patch cannot be applied cleanly
to the release.
The nVMX code isn't buggy, VMX instructions #UD in compatibility mode, and except
for VMCALL, that #UD has higher priority than VM-Exit interception.  So I'd say
just drop the nVMX side of things.
But it looks the old code doesn't unconditionally inject #UD when in
compatibility mode?
I think Sean means VMX instructions is not valid in compatibility mode
and it triggers #UD, which has higher priority than VM-Exit, by the
processor in non-root mode.

So if there is a VM-Exit due to VMX instruction , it is in 64-bit mode
for sure if it is in long mode.
Oh I see thanks.

Then is it better to add some comment to explain, or add a WARN() if it's not in
64-bit mode?

I also prefer to add a comment if no objection.

Seems I am not the only one who didn't get it  : )





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