Subject: Re: [PATCH kernel v2 1/6] KVM: PPC: Rework H_PUT_TCE/H_GET_TCE handlers

From: David Gibson <[email-masked]>
Date: Mon, 25 Jan 2016 10:43:29 +1100

On Fri, Jan 22, 2016 at 12:59:47PM +1100, Alexey Kardashevskiy wrote:
> On 01/22/2016 11:42 AM, David Gibson wrote:
> >On Thu, Jan 21, 2016 at 06:39:32PM +1100, Alexey Kardashevskiy wrote:
> >>This reworks the existing H_PUT_TCE/H_GET_TCE handlers to have following
> >>patches applied nicer.
> >>
> >>This moves the ioba boundaries check to a helper and adds a check for
> >>least bits which have to be zeros.
> >>
> >>The patch is pretty mechanical (only check for least ioba bits is added)
> >>so no change in behaviour is expected.
> >>
> >>Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> >
> >Concept looks good, but there are a couple of nits.
> >
> >>---
> >>Changelog:
> >>v2:
> >>* compare @ret with H_SUCCESS instead of assuming H_SUCCESS is zero
> >>* made error reporting cleaner
> >>---
> >>  arch/powerpc/kvm/book3s_64_vio_hv.c | 111 +++++++++++++++++++++++-------------
> >>  1 file changed, 72 insertions(+), 39 deletions(-)
> >>
> >>diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
> >>index 89e96b3..862f9a2 100644
> >>--- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> >>+++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> >>@@ -35,71 +35,104 @@
> >>  #include <asm/ppc-opcode.h>
> >>  #include <asm/kvm_host.h>
> >>  #include <asm/udbg.h>
> >>+#include <asm/iommu.h>
> >>
> >>  #define TCES_PER_PAGE	(PAGE_SIZE / sizeof(u64))
> >>
> >>+/*
> >>+ * Finds a TCE table descriptor by LIOBN.
> >>+ *
> >>+ * WARNING: This will be called in real or virtual mode on HV KVM and virtual
> >>+ *          mode on PR KVM
> >>+ */
> >>+static struct kvmppc_spapr_tce_table *kvmppc_find_table(struct kvm_vcpu *vcpu,
> >>+		unsigned long liobn)
> >>+{
> >>+	struct kvm *kvm = vcpu->kvm;
> >>+	struct kvmppc_spapr_tce_table *stt;
> >>+
> >>+	list_for_each_entry_lockless(stt, &kvm->arch.spapr_tce_tables, list)
> >
> >list_for_each_entry_lockless?  According to the comments in the
> >header, that's for RCU protected lists, whereas this one is just
> >protected by the lock in the kvm structure.  This is replacing a plain
> >list_for_each_entry().
> 
> My bad, the next patch should have done this
> s/list_for_each_entry/list_for_each_entry_lockless/

Ah, yes.  I hadn't yet looked at the second patch.

> >>+		if (stt->liobn == liobn)
> >>+			return stt;
> >>+
> >>+	return NULL;
> >>+}
> >>+
> >>+/*
> >>+ * Validates IO address.
> >>+ *
> >>+ * WARNING: This will be called in real-mode on HV KVM and virtual
> >>+ *          mode on PR KVM
> >>+ */
> >>+static long kvmppc_ioba_validate(struct kvmppc_spapr_tce_table *stt,
> >>+		unsigned long ioba, unsigned long npages)
> >>+{
> >>+	unsigned long mask = (1ULL << IOMMU_PAGE_SHIFT_4K) - 1;
> >>+	unsigned long idx = ioba >> IOMMU_PAGE_SHIFT_4K;
> >>+	unsigned long size = stt->window_size >> IOMMU_PAGE_SHIFT_4K;
> >>+
> >>+	if ((ioba & mask) || (idx + npages > size))
> >
> >It doesn't matter for the current callers, but you should check for
> >overflow in idx + npages as well.
> 
> 
> npages can be only 1..512 and this is checked in H_PUT_TCE/etc handlers.
> idx is 52bit long max.
> And this is not going to change because H_PUT_TCE_INDIRECT will always be
> limited by 512 (or one 4K page).

Ah, ok.

> Do I still need the overflow check here?

Hm, I guess it's not essential.  I'd still prefer to see it though,
since it's good practice in general.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson