* [PATCH v2] i386: Make 'hv-reenlightenment' require explicit 'tsc-frequency' setting
@ 2021-03-31 11:39 Vitaly Kuznetsov
2021-04-14 13:26 ` Eduardo Habkost
0 siblings, 1 reply; 5+ messages in thread
From: Vitaly Kuznetsov @ 2021-03-31 11:39 UTC (permalink / raw)
To: qemu-devel, Paolo Bonzini
Cc: Eduardo Habkost, David Edmondson, Michael S. Tsirkin,
Richard Henderson, Dr . David Alan Gilbert
Commit 561dbb41b1d7 "i386: Make migration fail when Hyper-V reenlightenment
was enabled but 'user_tsc_khz' is unset" forbade migrations with when guest
has opted for reenlightenment notifications but 'tsc-frequency' wasn't set
explicitly on the command line. This works but the migration fails late and
this may come as an unpleasant surprise. To make things more explicit,
require 'tsc-frequency=' on the command line when 'hv-reenlightenment' was
enabled. Make the change affect 6.0+ machine types only to preserve
previously-valid configurations.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
Changes since v1:
- Typos in commit message/comment fixed [David Edmondson]
- Add Acked-by tag [Dr. David Alan Gilbert]
---
docs/hyperv.txt | 1 +
hw/i386/pc.c | 1 +
target/i386/cpu.c | 23 +++++++++++++++++++++--
target/i386/cpu.h | 1 +
4 files changed, 24 insertions(+), 2 deletions(-)
diff --git a/docs/hyperv.txt b/docs/hyperv.txt
index e53c581f4586..5b02d341ab25 100644
--- a/docs/hyperv.txt
+++ b/docs/hyperv.txt
@@ -165,6 +165,7 @@ emulate TSC accesses after migration so 'tsc-frequency=' CPU option also has to
be specified to make migration succeed. The destination host has to either have
the same TSC frequency or support TSC scaling CPU feature.
+Requires: tsc-frequency
Recommended: hv-frequencies
3.16. hv-evmcs
diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 8a84b25a031e..47b79e949ad7 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -98,6 +98,7 @@
GlobalProperty pc_compat_5_2[] = {
{ "ICH9-LPC", "x-smi-cpu-hotunplug", "off" },
+ { TYPE_X86_CPU, "x-hv-reenlightenment-requires-tscfreq", "off"},
};
const size_t pc_compat_5_2_len = G_N_ELEMENTS(pc_compat_5_2);
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 6b3e9467f177..dbcd2ffbbbe5 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -6647,10 +6647,23 @@ static void x86_cpu_filter_features(X86CPU *cpu, bool verbose)
}
}
-static void x86_cpu_hyperv_realize(X86CPU *cpu)
+static void x86_cpu_hyperv_realize(X86CPU *cpu, Error **errp)
{
+ CPUX86State *env = &cpu->env;
size_t len;
+ /*
+ * Reenlightenment requires explicit 'tsc-frequency' setting for successful
+ * migration (see hyperv_reenlightenment_post_load()). As 'hv-passthrough'
+ * mode is not migratable, we can loosen the restriction.
+ */
+ if (hyperv_feat_enabled(cpu, HYPERV_FEAT_REENLIGHTENMENT) &&
+ !cpu->hyperv_passthrough && !env->user_tsc_khz &&
+ cpu->hyperv_reenlightenment_requires_tscfreq) {
+ error_setg(errp, "'hv-reenlightenment' requires 'tsc-frequency' to be set");
+ return;
+ }
+
/* Hyper-V vendor id */
if (!cpu->hyperv_vendor) {
memcpy(cpu->hyperv_vendor_id, "Microsoft Hv", 12);
@@ -6846,7 +6859,11 @@ static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
}
/* Process Hyper-V enlightenments */
- x86_cpu_hyperv_realize(cpu);
+ x86_cpu_hyperv_realize(cpu, &local_err);
+ if (local_err != NULL) {
+ error_propagate(errp, local_err);
+ return;
+ }
cpu_exec_realizefn(cs, &local_err);
if (local_err != NULL) {
@@ -7374,6 +7391,8 @@ static Property x86_cpu_properties[] = {
DEFINE_PROP_INT32("x-hv-max-vps", X86CPU, hv_max_vps, -1),
DEFINE_PROP_BOOL("x-hv-synic-kvm-only", X86CPU, hyperv_synic_kvm_only,
false),
+ DEFINE_PROP_BOOL("x-hv-reenlightenment-requires-tscfreq", X86CPU,
+ hyperv_reenlightenment_requires_tscfreq, true),
DEFINE_PROP_BOOL("x-intel-pt-auto-level", X86CPU, intel_pt_auto_level,
true),
DEFINE_PROP_END_OF_LIST()
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 570f916878f9..0196a300f018 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1677,6 +1677,7 @@ struct X86CPU {
uint32_t hyperv_spinlock_attempts;
char *hyperv_vendor;
bool hyperv_synic_kvm_only;
+ bool hyperv_reenlightenment_requires_tscfreq;
uint64_t hyperv_features;
bool hyperv_passthrough;
OnOffAuto hyperv_no_nonarch_cs;
--
2.30.2
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2] i386: Make 'hv-reenlightenment' require explicit 'tsc-frequency' setting
2021-03-31 11:39 [PATCH v2] i386: Make 'hv-reenlightenment' require explicit 'tsc-frequency' setting Vitaly Kuznetsov
@ 2021-04-14 13:26 ` Eduardo Habkost
2021-04-14 13:51 ` Vitaly Kuznetsov
0 siblings, 1 reply; 5+ messages in thread
From: Eduardo Habkost @ 2021-04-14 13:26 UTC (permalink / raw)
To: Vitaly Kuznetsov
Cc: Michael S. Tsirkin, David Edmondson, Richard Henderson,
qemu-devel, Dr . David Alan Gilbert, Paolo Bonzini
My apologies, this was lost under the noise in my mail inbox.
(I promise I'm trying to improve)
On Wed, Mar 31, 2021 at 01:39:48PM +0200, Vitaly Kuznetsov wrote:
> Commit 561dbb41b1d7 "i386: Make migration fail when Hyper-V reenlightenment
> was enabled but 'user_tsc_khz' is unset" forbade migrations with when guest
> has opted for reenlightenment notifications but 'tsc-frequency' wasn't set
> explicitly on the command line. This works but the migration fails late and
> this may come as an unpleasant surprise. To make things more explicit,
> require 'tsc-frequency=' on the command line when 'hv-reenlightenment' was
> enabled. Make the change affect 6.0+ machine types only to preserve
> previously-valid configurations.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Even if the 6.0 release gets delayed, I wouldn't be comfortable
including this in a -rc4.
What if the user does not plan to live migrate the machine at
all? Why is this case different from the ~25
migrate_add_blocker() calls in QEMU, where we block migration but
still let the VM run?
--
Eduardo
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] i386: Make 'hv-reenlightenment' require explicit 'tsc-frequency' setting
2021-04-14 13:26 ` Eduardo Habkost
@ 2021-04-14 13:51 ` Vitaly Kuznetsov
2021-04-14 14:39 ` Eduardo Habkost
0 siblings, 1 reply; 5+ messages in thread
From: Vitaly Kuznetsov @ 2021-04-14 13:51 UTC (permalink / raw)
To: Eduardo Habkost
Cc: Michael S. Tsirkin, David Edmondson, Richard Henderson,
qemu-devel, Dr . David Alan Gilbert, Paolo Bonzini
Eduardo Habkost <ehabkost@redhat.com> writes:
> My apologies, this was lost under the noise in my mail inbox.
> (I promise I'm trying to improve)
>
> On Wed, Mar 31, 2021 at 01:39:48PM +0200, Vitaly Kuznetsov wrote:
>> Commit 561dbb41b1d7 "i386: Make migration fail when Hyper-V reenlightenment
>> was enabled but 'user_tsc_khz' is unset" forbade migrations with when guest
>> has opted for reenlightenment notifications but 'tsc-frequency' wasn't set
>> explicitly on the command line. This works but the migration fails late and
>> this may come as an unpleasant surprise. To make things more explicit,
>> require 'tsc-frequency=' on the command line when 'hv-reenlightenment' was
>> enabled. Make the change affect 6.0+ machine types only to preserve
>> previously-valid configurations.
>>
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
> Even if the 6.0 release gets delayed, I wouldn't be comfortable
> including this in a -rc4.
>
> What if the user does not plan to live migrate the machine at
> all? Why is this case different from the ~25
> migrate_add_blocker() calls in QEMU, where we block migration but
> still let the VM run?
The question is when do we want to let the user know about the
problem. By refusing to start with 'hv-reenlightenment' and without
'tsc-frequency' we make it sure he knows early.
We can, indeed, replace this with migrate_add_blocker() call but the
fact that the VM is not migratable may come as a (late) surprise (we
can certainly print a warning but these may be hidden by upper layers).
Also, v1 of this patch was implementing a slightly different approach
failing the migration late if we can't set tsc frequency on the
destination host. Explicit 'tsc-frequency=' was not required.
Personally, I'm comfortable with any approach, please advise.
--
Vitaly
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] i386: Make 'hv-reenlightenment' require explicit 'tsc-frequency' setting
2021-04-14 13:51 ` Vitaly Kuznetsov
@ 2021-04-14 14:39 ` Eduardo Habkost
2021-04-15 9:31 ` Vitaly Kuznetsov
0 siblings, 1 reply; 5+ messages in thread
From: Eduardo Habkost @ 2021-04-14 14:39 UTC (permalink / raw)
To: Vitaly Kuznetsov
Cc: Michael S. Tsirkin, David Edmondson, Richard Henderson,
qemu-devel, Dr . David Alan Gilbert, Paolo Bonzini
On Wed, Apr 14, 2021 at 03:51:37PM +0200, Vitaly Kuznetsov wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
>
> > My apologies, this was lost under the noise in my mail inbox.
> > (I promise I'm trying to improve)
> >
> > On Wed, Mar 31, 2021 at 01:39:48PM +0200, Vitaly Kuznetsov wrote:
> >> Commit 561dbb41b1d7 "i386: Make migration fail when Hyper-V reenlightenment
> >> was enabled but 'user_tsc_khz' is unset" forbade migrations with when guest
> >> has opted for reenlightenment notifications but 'tsc-frequency' wasn't set
> >> explicitly on the command line. This works but the migration fails late and
> >> this may come as an unpleasant surprise. To make things more explicit,
> >> require 'tsc-frequency=' on the command line when 'hv-reenlightenment' was
> >> enabled. Make the change affect 6.0+ machine types only to preserve
> >> previously-valid configurations.
> >>
> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> >> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> >
> > Even if the 6.0 release gets delayed, I wouldn't be comfortable
> > including this in a -rc4.
> >
> > What if the user does not plan to live migrate the machine at
> > all? Why is this case different from the ~25
> > migrate_add_blocker() calls in QEMU, where we block migration but
> > still let the VM run?
>
> The question is when do we want to let the user know about the
> problem. By refusing to start with 'hv-reenlightenment' and without
> 'tsc-frequency' we make it sure he knows early.
>
> We can, indeed, replace this with migrate_add_blocker() call but the
> fact that the VM is not migratable may come as a (late) surprise (we
> can certainly print a warning but these may be hidden by upper layers).
>
> Also, v1 of this patch was implementing a slightly different approach
> failing the migration late if we can't set tsc frequency on the
> destination host. Explicit 'tsc-frequency=' was not required.
>
> Personally, I'm comfortable with any approach, please advise.
I agree with what you are trying to do, I just wonder why we
wouldn't do exactly the same for all other migrate_add_blocker()
calls too (whatever the solution we choose here).
I'd suggest the following:
- For people who use "-only-migratable", using
migrate_add_blocker() here already solves the problem.
- For people who don't use "-only-migratable", we could change
migrate_add_blocker() to print a warning by default (only on
machine types where live migration is supported).
- For people who don't need live migration and don't want to see
those warnings, we can introduce a "-no-migration" option.
--
Eduardo
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] i386: Make 'hv-reenlightenment' require explicit 'tsc-frequency' setting
2021-04-14 14:39 ` Eduardo Habkost
@ 2021-04-15 9:31 ` Vitaly Kuznetsov
0 siblings, 0 replies; 5+ messages in thread
From: Vitaly Kuznetsov @ 2021-04-15 9:31 UTC (permalink / raw)
To: Eduardo Habkost
Cc: Michael S. Tsirkin, David Edmondson, Richard Henderson,
qemu-devel, Dr . David Alan Gilbert, Paolo Bonzini
Eduardo Habkost <ehabkost@redhat.com> writes:
> On Wed, Apr 14, 2021 at 03:51:37PM +0200, Vitaly Kuznetsov wrote:
>> Eduardo Habkost <ehabkost@redhat.com> writes:
>>
>> > My apologies, this was lost under the noise in my mail inbox.
>> > (I promise I'm trying to improve)
>> >
>> > On Wed, Mar 31, 2021 at 01:39:48PM +0200, Vitaly Kuznetsov wrote:
>> >> Commit 561dbb41b1d7 "i386: Make migration fail when Hyper-V reenlightenment
>> >> was enabled but 'user_tsc_khz' is unset" forbade migrations with when guest
>> >> has opted for reenlightenment notifications but 'tsc-frequency' wasn't set
>> >> explicitly on the command line. This works but the migration fails late and
>> >> this may come as an unpleasant surprise. To make things more explicit,
>> >> require 'tsc-frequency=' on the command line when 'hv-reenlightenment' was
>> >> enabled. Make the change affect 6.0+ machine types only to preserve
>> >> previously-valid configurations.
>> >>
>> >> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> >> Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>> >
>> > Even if the 6.0 release gets delayed, I wouldn't be comfortable
>> > including this in a -rc4.
>> >
>> > What if the user does not plan to live migrate the machine at
>> > all? Why is this case different from the ~25
>> > migrate_add_blocker() calls in QEMU, where we block migration but
>> > still let the VM run?
>>
>> The question is when do we want to let the user know about the
>> problem. By refusing to start with 'hv-reenlightenment' and without
>> 'tsc-frequency' we make it sure he knows early.
>>
>> We can, indeed, replace this with migrate_add_blocker() call but the
>> fact that the VM is not migratable may come as a (late) surprise (we
>> can certainly print a warning but these may be hidden by upper layers).
>>
>> Also, v1 of this patch was implementing a slightly different approach
>> failing the migration late if we can't set tsc frequency on the
>> destination host. Explicit 'tsc-frequency=' was not required.
>>
>> Personally, I'm comfortable with any approach, please advise.
>
> I agree with what you are trying to do, I just wonder why we
> wouldn't do exactly the same for all other migrate_add_blocker()
> calls too (whatever the solution we choose here).
>
> I'd suggest the following:
>
> - For people who use "-only-migratable", using
> migrate_add_blocker() here already solves the problem.
>
> - For people who don't use "-only-migratable", we could change
> migrate_add_blocker() to print a warning by default (only on
> machine types where live migration is supported).
>
> - For people who don't need live migration and don't want to see
> those warnings, we can introduce a "-no-migration" option.
All make sense to me, let me try to draft v3 based on your proposal.
Thanks!
--
Vitaly
^ permalink raw reply [flat|nested] 5+ messages in thread
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2021-03-31 11:39 [PATCH v2] i386: Make 'hv-reenlightenment' require explicit 'tsc-frequency' setting Vitaly Kuznetsov
2021-04-14 13:26 ` Eduardo Habkost
2021-04-14 13:51 ` Vitaly Kuznetsov
2021-04-14 14:39 ` Eduardo Habkost
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