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Re: [Qemu-devel] [PATCH] ppc: fix ppc_set_compat() with KVM PR
From: |
David Gibson |
Subject: |
Re: [Qemu-devel] [PATCH] ppc: fix ppc_set_compat() with KVM PR |
Date: |
Tue, 15 Aug 2017 14:04:09 +1000 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
On Mon, Aug 14, 2017 at 07:49:16PM +0200, Greg Kurz wrote:
> When running in KVM PR mode, kvmppc_set_compat() always fail because the
> current PR implementation doesn't handle KVM_REG_PPC_ARCH_COMPAT. Now that
> the machine code inconditionally calls ppc_set_compat_all() at reset time
> to restore the compat mode default value (commit 66d5c492dd3a9), it is
> impossible to start a guest with PR:
>
> qemu-system-ppc64: Unable to set CPU compatibility mode in KVM:
> Invalid argument
>
> A tentative patch [1] was recently sent by Suraj to address the issue, but
> it would prevent the compat mode to be turned off on reset. And we really
> don't want to explicitely check for KVM PR. During the patch's review,
> David suggested that we should only call the KVM ioctl() if the compat
> PVR changes. This allows at least to run with KVM PR, provided no compat
> mode is requested from the command line (which should be the case when
> running PR nested). This is what this patch does.
I'm not sure that's true any more, since we now prefer compat modes
during CAS. I guess we could exclude the compat modes from the
advertised list based on what KVM supports, but that seems pretty
awkward.
> While here, we also fix the side effect where KVM would fail but we would
> change the CPU state in QEMU anyway.
>
> [1] http://patchwork.ozlabs.org/patch/782039/
>
> Signed-off-by: Greg Kurz <address@hidden>
In any case, this makes things better than they were, so I'm applying.
> ---
> target/ppc/compat.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/target/ppc/compat.c b/target/ppc/compat.c
> index f1b67faa97e3..f8729fe46d61 100644
> --- a/target/ppc/compat.c
> +++ b/target/ppc/compat.c
> @@ -140,16 +140,17 @@ void ppc_set_compat(PowerPCCPU *cpu, uint32_t
> compat_pvr, Error **errp)
>
> cpu_synchronize_state(CPU(cpu));
>
> - cpu->compat_pvr = compat_pvr;
> - env->spr[SPR_PCR] = pcr & pcc->pcr_mask;
> -
> - if (kvm_enabled()) {
> + if (kvm_enabled() && cpu->compat_pvr != compat_pvr) {
> int ret = kvmppc_set_compat(cpu, cpu->compat_pvr);
> if (ret < 0) {
> error_setg_errno(errp, -ret,
> "Unable to set CPU compatibility mode in KVM");
> + return;
> }
> }
> +
> + cpu->compat_pvr = compat_pvr;
> + env->spr[SPR_PCR] = pcr & pcc->pcr_mask;
> }
>
> typedef struct {
>
--
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
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