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Re: [PATCH 6/6] svm/nestedvm: Introduce nested capabilities bit
- To: George Dunlap <george.dunlap@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 22 Feb 2024 16:05:15 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jun Nakajima <jun.nakajima@xxxxxxxxx>, Kevin Tian <kevin.tian@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 22 Feb 2024 15:05:28 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22.02.2024 15:33, George Dunlap wrote:
> On Tue, Feb 20, 2024 at 12:25 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 06.02.2024 02:20, George Dunlap wrote:
>>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>>> @@ -3021,6 +3021,9 @@ const struct hvm_function_table * __init
>>> start_vmx(void)
>>> if ( cpu_has_vmx_tsc_scaling )
>>> vmx_function_table.tsc_scaling.ratio_frac_bits = 48;
>>>
>>> + /* TODO: Require hardware support before enabling nested virt */
>>> + vmx_function_table.caps.nested_virt = vmx_function_table.caps.hap;
>>
>> This won't have the intended effect if hap_supported() ends up clearing
>> the bit (used as input here) due to a command line option override. I
>> wonder if instead this wants doing e.g. in a new hook to be called from
>> nestedhvm_setup(). On the SVM side the hook function would then be the
>> start_nested_svm() that you already introduce, with a caps.hap check
>> added.
>
> I take it presmp_initcall()'s are guaranteed to run before __initcall()'s?
Yes - the former happen ahead of AP bringup, the latter after.
>> Since you leave the other nested-related if() in place in
>> arch_sanitise_domain_config(), all ought to be well, but I think that
>> other if() really wants replacing by the one you presently add.
>
> Ack.
>
> I'll probably check in patches 1,2,3, and 5, and resend the other two,
> unless you'd like to see all the changes again...
No need imo to re-post anything that was agreed upon.
Jan
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