* Re: [PATCH v2] KVM: PPC: Book3S PR: only install valid SLBs during KVM_SET_SREGS
2017-10-02 8:40 [PATCH v2] KVM: PPC: Book3S PR: only install valid SLBs during KVM_SET_SREGS Greg Kurz
@ 2017-10-03 0:49 ` David Gibson
2017-10-13 7:27 ` Greg Kurz
2017-10-14 2:49 ` Paul Mackerras
2 siblings, 0 replies; 4+ messages in thread
From: David Gibson @ 2017-10-03 0:49 UTC (permalink / raw)
To: Greg Kurz
Cc: kvm-ppc, qemu-ppc, linuxppc-dev, Michael Ellerman, Paul Mackerras
[-- Attachment #1: Type: text/plain, Size: 2383 bytes --]
On Mon, Oct 02, 2017 at 10:40:22AM +0200, Greg Kurz wrote:
> Userland passes an array of 64 SLB descriptors to KVM_SET_SREGS,
> some of which are valid (ie, SLB_ESID_V is set) and the rest are
> likely all-zeroes (with QEMU at least).
>
> Each of them is then passed to kvmppc_mmu_book3s_64_slbmte(), which
> assumes to find the SLB index in the 3 lower bits of its rb argument.
> When passed zeroed arguments, it happily overwrites the 0th SLB entry
> with zeroes. This is exactly what happens while doing live migration
> with QEMU when the destination pushes the incoming SLB descriptors to
> KVM PR. When reloading the SLBs at the next synchronization, QEMU first
> clears its SLB array and only restore valid ones, but the 0th one is
> now gone and we cannot access the corresponding memory anymore:
>
> (qemu) x/x $pc
> c0000000000b742c: Cannot access memory
>
> To avoid this, let's filter out non-valid SLB entries. While here, we
> also force a full SLB flush before installing new entries.
>
> Signed-off-by: Greg Kurz <groug@kaod.org>
Seems sensible to me.
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> v2: - flush SLB before installing new entries
> ---
> arch/powerpc/kvm/book3s_pr.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index 3beb4ff469d1..7cce08d610ae 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -1327,9 +1327,15 @@ static int kvm_arch_vcpu_ioctl_set_sregs_pr(struct kvm_vcpu *vcpu,
>
> vcpu3s->sdr1 = sregs->u.s.sdr1;
> if (vcpu->arch.hflags & BOOK3S_HFLAG_SLB) {
> + /* Flush all SLB entries */
> + vcpu->arch.mmu.slbmte(vcpu, 0, 0);
> + vcpu->arch.mmu.slbia(vcpu);
> +
> for (i = 0; i < 64; i++) {
> - vcpu->arch.mmu.slbmte(vcpu, sregs->u.s.ppc64.slb[i].slbv,
> - sregs->u.s.ppc64.slb[i].slbe);
> + u64 rb = sregs->u.s.ppc64.slb[i].slbe;
> + u64 rs = sregs->u.s.ppc64.slb[i].slbv;
> + if (rb & SLB_ESID_V)
> + vcpu->arch.mmu.slbmte(vcpu, rs, rb);
> }
> } else {
> for (i = 0; i < 16; i++) {
>
--
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
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2] KVM: PPC: Book3S PR: only install valid SLBs during KVM_SET_SREGS
2017-10-02 8:40 [PATCH v2] KVM: PPC: Book3S PR: only install valid SLBs during KVM_SET_SREGS Greg Kurz
2017-10-03 0:49 ` David Gibson
@ 2017-10-13 7:27 ` Greg Kurz
2017-10-14 2:49 ` Paul Mackerras
2 siblings, 0 replies; 4+ messages in thread
From: Greg Kurz @ 2017-10-13 7:27 UTC (permalink / raw)
To: kvm-ppc
Cc: qemu-ppc, linuxppc-dev, David Gibson, Michael Ellerman,
Paul Mackerras
Ping ?
On Mon, 02 Oct 2017 10:40:22 +0200
Greg Kurz <groug@kaod.org> wrote:
> Userland passes an array of 64 SLB descriptors to KVM_SET_SREGS,
> some of which are valid (ie, SLB_ESID_V is set) and the rest are
> likely all-zeroes (with QEMU at least).
>
> Each of them is then passed to kvmppc_mmu_book3s_64_slbmte(), which
> assumes to find the SLB index in the 3 lower bits of its rb argument.
> When passed zeroed arguments, it happily overwrites the 0th SLB entry
> with zeroes. This is exactly what happens while doing live migration
> with QEMU when the destination pushes the incoming SLB descriptors to
> KVM PR. When reloading the SLBs at the next synchronization, QEMU first
> clears its SLB array and only restore valid ones, but the 0th one is
> now gone and we cannot access the corresponding memory anymore:
>
> (qemu) x/x $pc
> c0000000000b742c: Cannot access memory
>
> To avoid this, let's filter out non-valid SLB entries. While here, we
> also force a full SLB flush before installing new entries.
>
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> v2: - flush SLB before installing new entries
> ---
> arch/powerpc/kvm/book3s_pr.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
> index 3beb4ff469d1..7cce08d610ae 100644
> --- a/arch/powerpc/kvm/book3s_pr.c
> +++ b/arch/powerpc/kvm/book3s_pr.c
> @@ -1327,9 +1327,15 @@ static int kvm_arch_vcpu_ioctl_set_sregs_pr(struct kvm_vcpu *vcpu,
>
> vcpu3s->sdr1 = sregs->u.s.sdr1;
> if (vcpu->arch.hflags & BOOK3S_HFLAG_SLB) {
> + /* Flush all SLB entries */
> + vcpu->arch.mmu.slbmte(vcpu, 0, 0);
> + vcpu->arch.mmu.slbia(vcpu);
> +
> for (i = 0; i < 64; i++) {
> - vcpu->arch.mmu.slbmte(vcpu, sregs->u.s.ppc64.slb[i].slbv,
> - sregs->u.s.ppc64.slb[i].slbe);
> + u64 rb = sregs->u.s.ppc64.slb[i].slbe;
> + u64 rs = sregs->u.s.ppc64.slb[i].slbv;
> + if (rb & SLB_ESID_V)
> + vcpu->arch.mmu.slbmte(vcpu, rs, rb);
> }
> } else {
> for (i = 0; i < 16; i++) {
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH v2] KVM: PPC: Book3S PR: only install valid SLBs during KVM_SET_SREGS
2017-10-02 8:40 [PATCH v2] KVM: PPC: Book3S PR: only install valid SLBs during KVM_SET_SREGS Greg Kurz
2017-10-03 0:49 ` David Gibson
2017-10-13 7:27 ` Greg Kurz
@ 2017-10-14 2:49 ` Paul Mackerras
2 siblings, 0 replies; 4+ messages in thread
From: Paul Mackerras @ 2017-10-14 2:49 UTC (permalink / raw)
To: Greg Kurz; +Cc: kvm-ppc, qemu-ppc, linuxppc-dev, David Gibson, Michael Ellerman
On Mon, Oct 02, 2017 at 10:40:22AM +0200, Greg Kurz wrote:
> Userland passes an array of 64 SLB descriptors to KVM_SET_SREGS,
> some of which are valid (ie, SLB_ESID_V is set) and the rest are
> likely all-zeroes (with QEMU at least).
>
> Each of them is then passed to kvmppc_mmu_book3s_64_slbmte(), which
> assumes to find the SLB index in the 3 lower bits of its rb argument.
> When passed zeroed arguments, it happily overwrites the 0th SLB entry
> with zeroes. This is exactly what happens while doing live migration
> with QEMU when the destination pushes the incoming SLB descriptors to
> KVM PR. When reloading the SLBs at the next synchronization, QEMU first
> clears its SLB array and only restore valid ones, but the 0th one is
> now gone and we cannot access the corresponding memory anymore:
>
> (qemu) x/x $pc
> c0000000000b742c: Cannot access memory
>
> To avoid this, let's filter out non-valid SLB entries. While here, we
> also force a full SLB flush before installing new entries.
With this, a 32-bit powermac config with PR KVM enabled fails to build:
CC [M] arch/powerpc/kvm/book3s_pr.o
/home/paulus/kernel/kvm/arch/powerpc/kvm/book3s_pr.c: In function ‘kvm_arch_vcpu_ioctl_set_sregs_pr’:
/home/paulus/kernel/kvm/arch/powerpc/kvm/book3s_pr.c:1337:13: error: ‘SLB_ESID_V’ undeclared (first use in this function)
if (rb & SLB_ESID_V)
^
/home/paulus/kernel/kvm/arch/powerpc/kvm/book3s_pr.c:1337:13: note: each undeclared identifier is reported only once for each function it appears in
/home/paulus/kernel/kvm/scripts/Makefile.build:313: recipe for target 'arch/powerpc/kvm/book3s_pr.o' failed
make[3]: *** [arch/powerpc/kvm/book3s_pr.o] Error 1
Paul.
^ permalink raw reply [flat|nested] 4+ messages in thread