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Re: [PATCH v5] x86: make Viridian support optional
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
- Date: Thu, 9 Oct 2025 19:33:55 +0300
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- Cc: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Alejandro Vallejo <alejandro.garciavallejo@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 09 Oct 2025 16:34:09 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.10.25 19:04, Jan Beulich wrote:
On 30.09.2025 14:52, Grygorii Strashko wrote:
--- a/xen/arch/x86/hvm/Kconfig
+++ b/xen/arch/x86/hvm/Kconfig
@@ -62,6 +62,16 @@ config ALTP2M
If unsure, stay with defaults.
+config VIRIDIAN
+ bool "Hyper-V enlightenments for guests" if EXPERT
+ default y
+ help
+ Support optimizations for Hyper-V guests such as faster hypercalls,
+ efficient timer and interrupt handling, and enhanced paravirtualized
+ I/O. This is to improve performance and compatibility of Windows VMs.
What is "paravirtualized I/O" about in this context?
It was phrased this way and agreed upon from the very beginning [1]
[1]
https://patchwork.kernel.org/project/xen-devel/patch/20250317071919.3766976-1-Sergiy_Kibrik@xxxxxxxx/#26305207
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -701,9 +701,12 @@ int hvm_domain_initialise(struct domain *d,
if ( hvm_tsc_scaling_supported )
d->arch.hvm.tsc_scaling_ratio = hvm_default_tsc_scaling_ratio;
- rc = viridian_domain_init(d);
- if ( rc )
- goto fail2;
+ if ( is_viridian_domain(d) )
+ {
+ rc = viridian_domain_init(d);
+ if ( rc )
+ goto fail2;
+ }
While this looks okay to me, ...
@@ -739,7 +742,8 @@ void hvm_domain_relinquish_resources(struct domain *d)
if ( hvm_funcs.nhvm_domain_relinquish_resources )
alternative_vcall(hvm_funcs.nhvm_domain_relinquish_resources, d);
- viridian_domain_deinit(d);
+ if ( is_viridian_domain(d) )
+ viridian_domain_deinit(d);
... I wonder if viridian_{domain,vcpu}_deinit() better wouldn't be tolerant
to be called anyway, thus avoiding the need for conditionals here and below
(and perhaps being a little more robust overall). Thoughts?
I think There are no limits for perfection. But at some point - need to stop.
Hence Viridian code will be removed from build when !VIRIDIAN - changing above
code will
require to add stubs for viridian_{domain,vcpu}_deinit().
FYI: Xen pipeline for this patch
https://gitlab.com/xen-project/people/dimaprkp4k/xen/-/pipelines/2090362213
--
Best regards,
-grygorii
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