On 1/31/25 18:32, Vishal Annapurve wrote:
...
> Are you hinting towards a model where TDX guest prohibits such call
> sites from being configured? I am not sure if it's a sustainable model
> if we just rely on the host not advertising these features as the
> guest kernel can still add new paths that are not controlled by the
> host that lead to *_safe_halt().
Let's say we required PARAVIRT_XXL for TDX guests and had TDX setup do:
static const typeof(pv_ops) tdx_irq_ops __initconst = {
.irq = {
.safe_halt = tdx_safe_halt,
},
};
We could get rid of a _bit_ of what TDX is doing now, like:
} else if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
pr_info("using TDX aware idle routine\n");
static_call_update(x86_idle, tdx_safe_halt);
and it would also fix this issue. Right?
This commit:
bfe6ed0c6727 ("x86/tdx: Add HLT support for TDX guests")
Makes it seem totally possible:
> Alternative choices like PV ops have been considered for adding
> safe_halt() support. But it was rejected because HLT paravirt calls
> only exist under PARAVIRT_XXL, and enabling it in TDX guest just for
> safe_halt() use case is not worth the cost.
and honestly it's seeming more "worth the cost" now since that partial
approach has a bug and might have more bugs in the future.
