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Re: [PATCH v2] x86/hvm: Add Kconfig option to disable nested virtualization
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 16 Feb 2026 09:57:50 +0100
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- Cc: Stefano Stabellini <stefano.stabellini@xxxxxxx>, roger.pau@xxxxxxxxxx, andrew.cooper3@xxxxxxxxxx, jason.andryuk@xxxxxxx, alejandro.garciavallejo@xxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 16 Feb 2026 08:57:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 13.02.2026 22:46, Stefano Stabellini wrote:
> On Mon, 9 Feb 2026, Jan Beulich wrote:
>> On 06.02.2026 22:05, Stefano Stabellini wrote:
>>> --- a/xen/arch/x86/sysctl.c
>>> +++ b/xen/arch/x86/sysctl.c
>>> @@ -103,6 +103,8 @@ void arch_do_physinfo(struct xen_sysctl_physinfo *pi)
>>> pi->capabilities |= XEN_SYSCTL_PHYSCAP_hap;
>>> if ( IS_ENABLED(CONFIG_SHADOW_PAGING) )
>>> pi->capabilities |= XEN_SYSCTL_PHYSCAP_shadow;
>>> + if ( hvm_nested_virt_supported() )
>>> + pi->capabilities |= XEN_SYSCTL_PHYSCAP_nestedhvm;
>>> }
>>>
>>> long arch_do_sysctl(
>>> --- a/xen/include/public/sysctl.h
>>> +++ b/xen/include/public/sysctl.h
>>> @@ -100,9 +100,11 @@ struct xen_sysctl_tbuf_op {
>>> /* Xen supports the Grant v1 and/or v2 ABIs. */
>>> #define XEN_SYSCTL_PHYSCAP_gnttab_v1 (1u << 8)
>>> #define XEN_SYSCTL_PHYSCAP_gnttab_v2 (1u << 9)
>>> +/* The platform supports nested HVM. */
>>> +#define XEN_SYSCTL_PHYSCAP_nestedhvm (1u << 10)
>>
>> Doesn't this want introducing up front, for the tool stack to make use of?
>
> What do you mean by "up front" in this context? In a separate toolstack
> patch?
Yes. Without the toolstack part the introduction of this flag is cosmetic
only, which isn't what we want.
Jan
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