linux-kernel - Re: [PATCH v2 11/12] x86/paravirt: Don't use pv

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Message-ID: <20250930083827.GI3245006@noisy.programming.kicks-ass.net>
Date: Tue, 30 Sep 2025 10:38:27 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Juergen Gross <jgross@...e.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	virtualization@...ts.linux.dev, xin@...or.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ajay Kaher <ajay.kaher@...adcom.com>,
	Alexey Makhalov <alexey.makhalov@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v2 11/12] x86/paravirt: Don't use pv_ops vector for MSR
 access functions

On Tue, Sep 30, 2025 at 09:03:55AM +0200, Juergen Gross wrote:

> +static __always_inline u64 read_msr(u32 msr)
> +{
> +	if (cpu_feature_enabled(X86_FEATURE_XENPV))
> +		return xen_read_msr(msr);
> +
> +	return native_rdmsrq(msr);
> +}
> +
> +static __always_inline int read_msr_safe(u32 msr, u64 *p)
> +{
> +	if (cpu_feature_enabled(X86_FEATURE_XENPV))
> +		return xen_read_msr_safe(msr, p);
> +
> +	return native_read_msr_safe(msr, p);
> +}
> +
> +static __always_inline void write_msr(u32 msr, u64 val)
> +{
> +	if (cpu_feature_enabled(X86_FEATURE_XENPV))
> +		xen_write_msr(msr, val);
> +	else
> +		native_wrmsrq(msr, val);
> +}
> +
> +static __always_inline int write_msr_safe(u32 msr, u64 val)
> +{
> +	if (cpu_feature_enabled(X86_FEATURE_XENPV))
> +		return xen_write_msr_safe(msr, val);
> +
> +	return native_write_msr_safe(msr, val);
> +}
> +
> +static __always_inline u64 rdpmc(int counter)
> +{
> +	if (cpu_feature_enabled(X86_FEATURE_XENPV))
> +		return xen_read_pmc(counter);
> +
> +	return native_read_pmc(counter);
> +}

Egads, didn't we just construct giant ALTERNATIVE()s for the native_
things? Why wrap that in a cpu_feature_enabled() instead of just adding
one more case to the ALTERNATIVE() ?