Re: [PATCH v2 03/15] KVM: x86/xen: Don't truncate RAX when handling hypercall from protected guest

[Binbin Wu]

On 5/18/2026 3:15 PM, David Woodhouse wrote:
> On Mon, 2026-05-18 at 10:19 +0800, Binbin Wu wrote:
>>  
>>>>>   	longmode = is_64_bit_hypercall(vcpu);
>>>>
>>>> Is the variable name misleading?
>>>
>>> It most definitely is.  However, @longmode is passed around quite a few locations
>>> in xen.c, and so I don't want to opportunistically fix this one variable.  Though
>>> I'm definitely not opposed to a separate patch to rename them all to is_64bit or
>>> something.
>>
>> OK, I can do it.
> 
> This one (as shown above) is clearly indicating whether this particular
> vCPU is in 64-bit mode for this particular hypercall. Changing that to
> is_64bit makes sense.
> 
> However, there is a separate overall mode for the VM, which is stored
> in 'kvm->arch.xen.long_mode' and accessed by userspace using the
> KVM_XEN_ATTR_TYPE_LONG_MODE attribute. It affects the datatypes used by
> shared memory data structures, and is also latched by the kernel when
> the guest writes the MSR for the hypercall page. That one should
> probably keep its name.

For this one, I think the current KVM code is consistent.
The format is determined by EFER.LMA, whether the guest is running in 64 bit or
compatible mode doesn't change the ABI.

struct compat_shared_info is used only when the guest is running natively in a
32-bit build.

> 
>