[2/8] KVM: pfncache: add a mark-dirty helper
Commit Message
From: Paul Durrant <pdurrant@amazon.com>
At the moment pages are marked dirty by open-coded calls to
mark_page_dirty_in_slot(), directly deferefencing the gpa and memslot
from the cache. After a subsequent patch these may not always be set
so add a helper now so that caller will protected from need to know
about this detail.
Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: x86@kernel.org
---
arch/x86/kvm/x86.c | 2 +-
arch/x86/kvm/xen.c | 13 ++++++-------
include/linux/kvm_host.h | 7 +++++++
virt/kvm/pfncache.c | 6 ++++++
4 files changed, 20 insertions(+), 8 deletions(-)
Comments
On Thu, 2023-09-14 at 11:34 +0200, Paul Durrant wrote:
> On 14/09/2023 10:21, David Woodhouse wrote:
> > On Thu, 2023-09-14 at 08:49 +0000, Paul Durrant wrote:
> > > --- a/arch/x86/kvm/xen.c
> > > +++ b/arch/x86/kvm/xen.c
> > > @@ -430,14 +430,13 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
> > > smp_wmb();
> > > }
> > >
> > > - if (user_len2)
> > > + if (user_len2) {
> > > + kvm_gpc_mark_dirty(gpc2);
> > > read_unlock(&gpc2->lock);
> > > + }
> > >
> > > + kvm_gpc_mark_dirty(gpc1);
> > > read_unlock_irqrestore(&gpc1->lock, flags);
> > > -
> > > - mark_page_dirty_in_slot(v->kvm, gpc1->memslot, gpc1->gpa >> PAGE_SHIFT);
> > > - if (user_len2)
> > > - mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
> > > }
> > >
> > > void kvm_xen_update_runstate(struct kvm_vcpu *v, int state)
> >
> > ISTR there was a reason why the mark_page_dirty_in_slot() was called
> > *after* unlocking. Although now I say it, that seems wrong... is that
> > because the spinlock is only protecting the uHVA→kHVA mapping, while
> > the memslot/gpa are going to remain valid even after unlock, because
> > those are protected by sRCU?
>
> Without the lock you could see an inconsistent GPA and memslot so I
> think you could theoretically calculate a bogus rel_gfn and walk off the
> end of the dirty bitmap. Hence moving the call inside the lock while I
> was in the neighbourhood seemed like a good idea. I could call it out in
> the commit comment if you'd like.
Yeah, I can't see a reason why it needs to be outside the lock, and as
you note, there really is a reason why it should be *inside*. Whatever
reason there was, it either disappeared in the revisions of the gpc
patch set or it was stupidity on my part in the first place.
So yeah, let it move inside the lock, call that out in the commit
message (I did note some of the other commits could have used a 'No
functional change intended' too, FWIW), and
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Thanks.
@@ -3137,7 +3137,7 @@ static void kvm_setup_guest_pvclock(struct kvm_vcpu *v,
guest_hv_clock->version = ++vcpu->hv_clock.version;
- mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
+ kvm_gpc_mark_dirty(gpc);
read_unlock_irqrestore(&gpc->lock, flags);
trace_kvm_pvclock_update(v->vcpu_id, &vcpu->hv_clock);
@@ -430,14 +430,13 @@ static void kvm_xen_update_runstate_guest(struct kvm_vcpu *v, bool atomic)
smp_wmb();
}
- if (user_len2)
+ if (user_len2) {
+ kvm_gpc_mark_dirty(gpc2);
read_unlock(&gpc2->lock);
+ }
+ kvm_gpc_mark_dirty(gpc1);
read_unlock_irqrestore(&gpc1->lock, flags);
-
- mark_page_dirty_in_slot(v->kvm, gpc1->memslot, gpc1->gpa >> PAGE_SHIFT);
- if (user_len2)
- mark_page_dirty_in_slot(v->kvm, gpc2->memslot, gpc2->gpa >> PAGE_SHIFT);
}
void kvm_xen_update_runstate(struct kvm_vcpu *v, int state)
@@ -543,13 +542,13 @@ void kvm_xen_inject_pending_events(struct kvm_vcpu *v)
: "0" (evtchn_pending_sel32));
WRITE_ONCE(vi->evtchn_upcall_pending, 1);
}
+
+ kvm_gpc_mark_dirty(gpc);
read_unlock_irqrestore(&gpc->lock, flags);
/* For the per-vCPU lapic vector, deliver it as MSI. */
if (v->arch.xen.upcall_vector)
kvm_xen_inject_vcpu_vector(v);
-
- mark_page_dirty_in_slot(v->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
}
int __kvm_xen_has_interrupt(struct kvm_vcpu *v)
@@ -1367,6 +1367,13 @@ int kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, unsigned long len);
*/
void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
+/**
+ * kvm_gpc_mark_dirty - mark a cached page as dirty.
+ *
+ * @gpc: struct gfn_to_pfn_cache object.
+ */
+void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc);
+
void kvm_sigset_activate(struct kvm_vcpu *vcpu);
void kvm_sigset_deactivate(struct kvm_vcpu *vcpu);
@@ -386,6 +386,12 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len)
}
EXPORT_SYMBOL_GPL(kvm_gpc_activate);
+void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
+{
+ mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
+}
+EXPORT_SYMBOL_GPL(kvm_gpc_mark_dirty);
+
void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc)
{
struct kvm *kvm = gpc->kvm;