From: Claudio Imbrenda <imbrenda@linux.ibm.com>
To: Nico Boehr <nrb@linux.ibm.com>
Cc: kvm@vger.kernel.org, frankja@linux.ibm.com, borntraeger@linux.ibm.com
Subject: Re: [PATCH v3 1/2] KVM: s390: pv: don't allow userspace to set the clock under PV
Date: Wed, 5 Oct 2022 19:01:17 +0200 [thread overview]
Message-ID: <20221005190117.5d7fe882@p-imbrenda> (raw)
In-Reply-To: <20221005163258.117232-2-nrb@linux.ibm.com>
On Wed, 5 Oct 2022 18:32:57 +0200
Nico Boehr <nrb@linux.ibm.com> wrote:
> When running under PV, the guest's TOD clock is under control of the
> ultravisor and the hypervisor isn't allowed to change it. Hence, don't
> allow userspace to change the guest's TOD clock by returning
> -EOPNOTSUPP.
>
> When userspace changes the guest's TOD clock, KVM updates its
> kvm.arch.epoch field and, in addition, the epoch field in all state
> descriptions of all VCPUs.
>
> But, under PV, the ultravisor will ignore the epoch field in the state
> description and simply overwrite it on next SIE exit with the actual
> guest epoch. This leads to KVM having an incorrect view of the guest's
> TOD clock: it has updated its internal kvm.arch.epoch field, but the
> ultravisor ignores the field in the state description.
>
> Whenever a guest is now waiting for a clock comparator, KVM will
> incorrectly calculate the time when the guest should wake up, possibly
> causing the guest to sleep for much longer than expected.
>
> With this change, kvm_s390_set_tod() will now take the kvm->lock to be
> able to call kvm_s390_pv_is_protected(). Since kvm_s390_set_tod_clock()
> also takes kvm->lock, use __kvm_s390_set_tod_clock() instead.
>
> Fixes: 0f3035047140 ("KVM: s390: protvirt: Do only reset registers that are accessible")
> Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
> Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
> arch/s390/kvm/kvm-s390.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index b7ef0b71014d..0a8019b14c8f 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -1207,6 +1207,8 @@ static int kvm_s390_vm_get_migration(struct kvm *kvm,
> return 0;
> }
>
> +static void __kvm_s390_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clock *gtod);
> +
> static int kvm_s390_set_tod_ext(struct kvm *kvm, struct kvm_device_attr *attr)
> {
> struct kvm_s390_vm_tod_clock gtod;
> @@ -1216,7 +1218,7 @@ static int kvm_s390_set_tod_ext(struct kvm *kvm, struct kvm_device_attr *attr)
>
> if (!test_kvm_facility(kvm, 139) && gtod.epoch_idx)
> return -EINVAL;
> - kvm_s390_set_tod_clock(kvm, >od);
> + __kvm_s390_set_tod_clock(kvm, >od);
>
> VM_EVENT(kvm, 3, "SET: TOD extension: 0x%x, TOD base: 0x%llx",
> gtod.epoch_idx, gtod.tod);
> @@ -1247,7 +1249,7 @@ static int kvm_s390_set_tod_low(struct kvm *kvm, struct kvm_device_attr *attr)
> sizeof(gtod.tod)))
> return -EFAULT;
>
> - kvm_s390_set_tod_clock(kvm, >od);
> + __kvm_s390_set_tod_clock(kvm, >od);
> VM_EVENT(kvm, 3, "SET: TOD base: 0x%llx", gtod.tod);
> return 0;
> }
> @@ -1259,6 +1261,12 @@ static int kvm_s390_set_tod(struct kvm *kvm, struct kvm_device_attr *attr)
> if (attr->flags)
> return -EINVAL;
>
> + mutex_lock(&kvm->lock);
> + if (kvm_s390_pv_is_protected(kvm)) {
> + ret = -EOPNOTSUPP;
> + goto out_unlock;
> + }
> +
> switch (attr->attr) {
> case KVM_S390_VM_TOD_EXT:
> ret = kvm_s390_set_tod_ext(kvm, attr);
> @@ -1273,6 +1281,9 @@ static int kvm_s390_set_tod(struct kvm *kvm, struct kvm_device_attr *attr)
> ret = -ENXIO;
> break;
> }
> +
> +out_unlock:
> + mutex_unlock(&kvm->lock);
> return ret;
> }
>
next prev parent reply other threads:[~2022-10-05 17:02 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-05 16:32 [PATCH v3 0/2] KVM: s390: pv: fix clock comparator late after suspend/resume Nico Boehr
2022-10-05 16:32 ` [PATCH v3 1/2] KVM: s390: pv: don't allow userspace to set the clock under PV Nico Boehr
2022-10-05 17:01 ` Claudio Imbrenda [this message]
2022-10-10 15:20 ` Janosch Frank
2022-10-11 8:41 ` Nico Boehr
2022-10-05 16:32 ` [PATCH v3 2/2] KVM: s390: remove now unused function kvm_s390_set_tod_clock Nico Boehr
2022-10-05 17:01 ` Claudio Imbrenda
2022-10-10 15:23 ` Janosch Frank
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20221005190117.5d7fe882@p-imbrenda \
--to=imbrenda@linux.ibm.com \
--cc=borntraeger@linux.ibm.com \
--cc=frankja@linux.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=nrb@linux.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).