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Re: [XEN][PATCH v3] x86: make Viridian support optional
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Grygorii Strashko <grygorii_strashko@xxxxxxxx>
- Date: Thu, 18 Sep 2025 20:17:44 +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, 18 Sep 2025 17:18:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18.09.25 18:41, Jan Beulich wrote:
On 16.09.2025 15:41, 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 HVM_VIRIDIAN
I may have said so already on v1: I'm not quite convinced of the need
or usefulness of the HVM_ part here. Viridian necessarily means HVM,
aiui.
sure.
--- a/xen/arch/x86/hvm/viridian/viridian.c
+++ b/xen/arch/x86/hvm/viridian/viridian.c
@@ -1116,14 +1116,14 @@ static int cf_check viridian_save_domain_ctxt(
{
const struct domain *d = v->domain;
const struct viridian_domain *vd = d->arch.hvm.viridian;
- struct hvm_viridian_domain_context ctxt = {
- .hypercall_gpa = vd->hypercall_gpa.raw,
- .guest_os_id = vd->guest_os_id.raw,
- };
+ struct hvm_viridian_domain_context ctxt = {};
if ( !is_viridian_domain(d) )
return 0;
This check doesn't check for vd being non-NULL, so this still feels a little
fragile, even if it looks correct now.
Hm. May be I missing smth., but
- if is_viridian_domain(d) and viridian_domain_init() succeeded
then d->arch.hvm.viridian != NULL, like always
(otherwise domain will not be created)
- if !is_viridian_domain() then code will not go further
so I'm missing to see how !d->arch.hvm.viridian (!vd) can happen here.
To be paranoid can also add:
if (!vd)
return -EINVAL;
+ ctxt.hypercall_gpa = vd->hypercall_gpa.raw;
+ ctxt.guest_os_id = vd->guest_os_id.raw,
+
viridian_time_save_domain_ctxt(d, &ctxt);
viridian_synic_save_domain_ctxt(d, &ctxt);
Just below here we have viridian_load_domain_ctxt(), which I'm pretty sure
now also needs to gain some check: Save records coming from user space, we
can't really rely on there being none of this type for a non-Viridian domain.
As per my understanding:
viridian_load_domain_ctxt() calls hvm_load_entry_zeroextend() which
should not succeed if context was not saved (which shouldn't happen for
!is_viridian_domain(d) case).
To be paranoid can also add in
viridian_load_domain_ctxt/viridian_load_vcpu_ctxt:
if ( !is_viridian_domain(d) )
return -ENODEV;
--
Best regards,
-grygorii
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