Re: [PATCH v10 04/27] x86/fpu/xstate: Introduce XFEATURE_MASK_KERNEL_DYNAMIC xfeature set

[Sean Christopherson]

On Sun, Feb 18, 2024, Yang Weijiang wrote:
> Define a new XFEATURE_MASK_KERNEL_DYNAMIC mask to specify the features

I still don't understand why this is being called DYNAMIC.  CET_SS isn't dynamic,
as KVM is _always_ allowed to save/restore CET_SS, i.e. whether or not KVM can
expose CET_SS to a guest is a static, boot-time decision.  Whether or not a guest
XSS actually enables CET_SS is "dynamic", but that's true of literally every
xfeature in XCR0 and XSS.

XFEATURE_MASK_XTILE_DATA is labeled as dynamic because userspace has to explicitly
request that XTILE_DATA be enabled, and thus whether or not KVM is allowed to
expose XTILE_DATA to the guest is a dynamic, runtime decision.

So IMO, the umbrella macro should be XFEATURE_MASK_KERNEL_GUEST_ONLY.