Attachment 247769 Details for Bug 276421 – Proposed fix

[patch] Proposed fix

0001-x86-cpu-improve-hypervisor-detection.patch (text/plain), 2.09 KB, created by Roger Pau Monné on 2024-01-19 09:27:44 UTC

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Creator: Roger Pau Monné

Created: 2024-01-19 09:27:44 UTC

Size: 2.09 KB

patch

obsolete

>From 87ad76a2501bbc3f4b5b8bf26a0b39f51fc1f447 Mon Sep 17 00:00:00 2001
>From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= <royger@FreeBSD.org>
>Date: Fri, 19 Jan 2024 10:15:17 +0100
>Subject: [PATCH] x86/cpu: improve hypervisor detection
>
>Some hypervisors can expose multiple signatures, for example Xen will expose
>both the Xen and the HyperV signatures if Viridian extensions are enabled for
>the guest.  Presence of multiple signatures is currently not handled by
>FreeBSD, that will exit once a known signature is found in cpuid output.
>
>Exposing the HyperV signature on hypervisors different than HyperV is not
>uncommon, this is done so that such hypervisor can expose a (subset) of the
>Viridian extensions to Windows guests for performance reasons.
>
>Fix the specific case of HyperV by not exiting from the scan if the HperV
>signature is found, and prefer a second signature if one is found.
>
>Note that long term we might wish to convert vm_guest into a bitmap, so that it
>can signal detection of multiple hypervisor interfaces.
>
>This allows to boot a FreeBSD guest using the Xen PV interfaces when the
>Viridian extensions are enabled in Xen.
>
>Fixes: b0165dc4539f ('x86/xen: fix HVM guest hypercall page setup')
>PR: 276421
>Sponsored by: Cloud Software Group
>---
> sys/x86/x86/identcpu.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
>diff --git a/sys/x86/x86/identcpu.c b/sys/x86/x86/identcpu.c
>index 9c82f9f8a882..71ef7f648e14 100644
>--- a/sys/x86/x86/identcpu.c
>+++ b/sys/x86/x86/identcpu.c
>@@ -1409,7 +1409,18 @@ identify_hypervisor_cpuid_base(void)
> 				 * If we found a specific hypervisor, then
> 				 * we are finished.
> 				 */
>-				if (vm_guest != VM_GUEST_VM)
>+				if (vm_guest != VM_GUEST_VM &&
>+				    /*
>+				     * Xen and other hypervisors can expose the
>+				     * HyperV signature in addition to the
>+				     * native one in order to support Viridian
>+				     * extensions for Windows guests.
>+				     *
>+				     * Do the full cpuid scan if HyperV is
>+				     * detected, as the native hypervisor is
>+				     * preferred.
>+				     */
>+				    vm_guest != VM_GUEST_HV)
> 					return;
> 			}
> 		}
>-- 
>2.43.0
>

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