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Re: [PATCH 2/6] vVMX: adjust reg_read() for 32-bit guests
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 11 Jun 2025 13:16:58 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 11 Jun 2025 11:17:04 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 11.06.2025 13:07, Andrew Cooper wrote:
> On 11/06/2025 11:42 am, Jan Beulich wrote:
>> Using the full 64-bit register values is wrong in this case; especially
>> soon after a mode switch from long mode to 32-bit one upper halves of
>> registers may continue to be non-zero.
>>
>> Fixes: 09fce8016596 ("Nested VMX: Emulation of guest VMXON/OFF instruction")
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> Note that the affected VMX insns are invalid to use from compatibility
>> mode, and hence the more expensive vmx_guest_x86_mode() doesn't need
>> using here.
>
> Fine, but you must have a comment to this effect in the code, and what
> prevents compatibility mode getting here?
Sure, I can add a comment there. As to compatibility mode - the insns will
#UD, and hence no (instruction based) VMEXIT will occur.
Jan
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