linux-kernel - Re: [PATCH] xen/acpi: allow xen-acpi-processor driver to load on Xen 4.7

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Date:	Fri, 8 Jul 2016 13:29:38 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Jan Beulich <JBeulich@...e.com>, <boris.ostrovsky@...cle.com>,
	"Juergen Gross" <JGross@...e.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen/acpi: allow xen-acpi-processor driver to load on Xen
 4.7

On 08/07/16 13:15, Jan Beulich wrote:
> As of Xen 4.7 PV CPUID doesn't expose either of CPUID[1].ECX[7] and
> CPUID[0x80000007].EDX[7] anymore, causing the driver to fail to load on
> both Intel and AMD systems. Doing any kind of hardware capability
> checks in the driver as a prerequisite was wrong anyway: With the
> hypervisor being in charge, all such checking should be done by it. If
> ACPI data gets uploaded despite some missing capability, the hypervisor
> is free to ignore part or all of that data.
> 
> Ditch the entire check_prereq() function, and do the only valid check
> (xen_initial_domain()) in the caller in its place.

Thanks, but I'm not sure this is sufficient.  I think the generic ACPI
code needs to know the full capabilities in order to generate the
correct tables, or you won't get (for example) turbo mode working.

We had to fake the EST feature back in.

--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -448,7 +448,8 @@ static void __init xen_init_cpuid_mask(void)
 	if ((cx & xsave_mask) != xsave_mask)
 		cpuid_leaf1_ecx_mask &= ~xsave_mask; /* disable XSAVE & OSXSAVE */
 	if (xen_check_mwait())
-		cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32));
+		cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32)
+					   | 1 << (X86_FEATURE_EST % 32));
 }

 static void xen_set_debugreg(int reg, unsigned long val)

David