Re: [PATCH] spapr: Handle HPT allocation failure in nested guest
On Fri, Sep 11, 2020 at 01:31:23AM -0300, Fabiano Rosas wrote:
> The nested KVM code does not yet support HPT guests. Calling the
> KVM_CAP_PPC_ALLOC_HTAB ioctl currently leads to KVM setting the guest
> as HPT and erroneously executing code in L1 that should only run in
> hypervisor mode, leading to an exception in the L1 vcpu thread when it
> enters the nested guest.
>
> This can be reproduced with -machine max-cpu-compat=power8 in the L2
> guest command line.
>
> The KVM code has since been modified to fail the ioctl when running in
> a nested environment so QEMU needs to be able to handle that. This
> patch provides an error message informing the user about the lack of
> support for HPT in nested guests.
>
> Signed-off-by: Fabiano Rosas
Applied to ppc-for-5.2.
> ---
> hw/ppc/spapr.c | 6 ++
> 1 file changed, 6 insertions(+)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 9bce1892b5..ea2c755310 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1483,6 +1483,12 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr,
> int shift,
> spapr_free_hpt(spapr);
>
> rc = kvmppc_reset_htab(shift);
> +
> +if (rc == -EOPNOTSUPP) {
> +error_setg(errp, "HPT not supported in nested guests");
> +return;
> +}
> +
> if (rc < 0) {
> /* kernel-side HPT needed, but couldn't allocate one */
> error_setg_errno(errp, errno,
--
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Re: [PATCH] spapr: Handle HPT allocation failure in nested guest
Fabiano Rosas writes:
> The nested KVM code does not yet support HPT guests. Calling the
> KVM_CAP_PPC_ALLOC_HTAB ioctl currently leads to KVM setting the guest
> as HPT and erroneously executing code in L1 that should only run in
> hypervisor mode, leading to an exception in the L1 vcpu thread when it
> enters the nested guest.
>
> This can be reproduced with -machine max-cpu-compat=power8 in the L2
> guest command line.
>
> The KVM code has since been modified to fail the ioctl when running in
> a nested environment so QEMU needs to be able to handle that. This
> patch provides an error message informing the user about the lack of
> support for HPT in nested guests.
>
I forgot to add a:
Reported-by: Satheesh Rajendran
> Signed-off-by: Fabiano Rosas
> ---
> hw/ppc/spapr.c | 6 ++
> 1 file changed, 6 insertions(+)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 9bce1892b5..ea2c755310 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1483,6 +1483,12 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr,
> int shift,
> spapr_free_hpt(spapr);
>
> rc = kvmppc_reset_htab(shift);
> +
> +if (rc == -EOPNOTSUPP) {
> +error_setg(errp, "HPT not supported in nested guests");
> +return;
> +}
> +
> if (rc < 0) {
> /* kernel-side HPT needed, but couldn't allocate one */
> error_setg_errno(errp, errno,
Re: [PATCH] spapr: Handle HPT allocation failure in nested guest
On Fri, 11 Sep 2020 01:31:23 -0300
Fabiano Rosas wrote:
> The nested KVM code does not yet support HPT guests. Calling the
> KVM_CAP_PPC_ALLOC_HTAB ioctl currently leads to KVM setting the guest
> as HPT and erroneously executing code in L1 that should only run in
> hypervisor mode, leading to an exception in the L1 vcpu thread when it
> enters the nested guest.
>
> This can be reproduced with -machine max-cpu-compat=power8 in the L2
> guest command line.
>
> The KVM code has since been modified to fail the ioctl when running in
Well, this isn't technically true for now. The KVM patch hasn't been merged
yet, but I guess it's okay to merge the QEMU patch anyway since it shouldn't
break older KVMs.
> a nested environment so QEMU needs to be able to handle that. This
> patch provides an error message informing the user about the lack of
> support for HPT in nested guests.
>
> Signed-off-by: Fabiano Rosas
> ---
> hw/ppc/spapr.c | 6 ++
> 1 file changed, 6 insertions(+)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index 9bce1892b5..ea2c755310 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -1483,6 +1483,12 @@ void spapr_reallocate_hpt(SpaprMachineState *spapr,
> int shift,
> spapr_free_hpt(spapr);
>
> rc = kvmppc_reset_htab(shift);
> +
> +if (rc == -EOPNOTSUPP) {
As noted on the kvm-ppc list, from a POSIX standpoint it seems that
ENOTSUP would be more appropriate... but since linux only knows
about EOPNOTSUPP and it has an unrelated and poorly named ENOTSUPP,
I guess it is okay to keep EOPNOTSUPP for the sake of consistency.
Reviewed-by: Greg Kurz
> +error_setg(errp, "HPT not supported in nested guests");
> +return;
> +}
> +
> if (rc < 0) {
> /* kernel-side HPT needed, but couldn't allocate one */
> error_setg_errno(errp, errno,
