Re: [PATCH v8 5/7] x86/sev: Add interface to re-enable RMP optimizations.

[Dave Hansen]

On 6/15/26 12:49, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
> 
> RMPOPT table is a per-CPU table which indicates if 1GB regions of
> physical memory are entirely hypervisor-owned or not.
> 
> When performing host memory accesses in hypervisor mode as well as
> non-SNP guest mode, the processor may consult the RMPOPT table to
> potentially skip an RMP access and improve performance.
> 
> Events such as RMPUPDATE can clear RMP optimizations. Add an interface
> to re-enable those optimizations.

This doesn't really help me understand when or how this function might
be called.

	Normal guest evens like splitting and collapsing large pages can
	clear RMP optimizations. Without some intervention, all RMP
	optimizations would eventually be lost. Periodically re-optimize
	the system.

> The interface uses mod_delayed_work() instead of queue_delayed_work()
> so that the delay timer is reset on each call. This provides proper
> batching semantics: re-optimization runs 10 seconds after the *last*
> VM termination rather than after the first. mod_delayed_work() also
> re-queues work that is already in-flight, so a re-scan request
> during an active scan is not silently dropped.

This seems sane.

> +void snp_rmpopt_all_physmem(void)
> +{
> +	if (!cpu_feature_enabled(X86_FEATURE_RMPOPT) || !rmpopt_configured)
> +		return;
> +
> +	guard(mutex)(&rmpopt_wq_mutex);
> +
> +	if (!rmpopt_wq)
> +		return;
> +
> +	mod_delayed_work(rmpopt_wq, &rmpopt_delayed_work,
> +			 msecs_to_jiffies(RMPOPT_WORK_TIMEOUT));
> +}
> +EXPORT_SYMBOL_GPL(snp_rmpopt_all_physmem);

Does this need to be globally exported? Or can it be exported to a
single module namespace?

I'm close to being able to ack this, but it's still got a few too many
nits to ack.