Re: [PATCH] spapr: nested: Add support for DPDES SPR in GSB for TCG L0

[Harsh Prateek Bora <harshpb@linux.ibm.com>]

Hi Amit,

On 10/17/24 16:30, Amit Machhiwal wrote:
> The DPDES support for doorbell emulation and handling for KVM on PAPR
> guests was added in Linux via [1]. Subsequently, a new GSB element for
> DPDES was added in Linux; the same has been missing in QEMU L0. Add

s/QEMU L0/ TCG L0 implementation?

> support for DPDES register's APIv2 GSB element and required handling in
> `spapr_nested.c`.
> 
> Currently, booting a KVM guest inside a QEMU TCG guest fails with the
> below crash. The crash is encountered when GUEST_RUN_VCPU hcall made
> into QEMU TCG L0 fails because H_INVALID_ELEMENT_VALUE is returned as
> the mapping of the element ID corresponding to DPDES (unknown to QEMU
> TCG L0) in GSR (Guest State Request) of TCG guest's KVM to the GSB
> (Guest State Buffer) elements of QEMU TCG L0 fails.

GSB full form would be more appropriate along with first mention of GSB 
in above text.

With that:
Reviewed-by: Harsh Prateek Bora <harshpb@linux.ibm.com>

> 
>   KVM: unknown exit, hardware reason ffffffffffffffea
>   NIP 0000000000000100   LR 0000000000000000 CTR 0000000000000000 XER 0000000000000000 CPU#0
>   MSR 0000000000003000 HID0 0000000000000000  HF 6c002000 iidx 3 didx 3
>   TB 00000000 00000000 DECR 0
>   GPR00 0000000000000000 0000000000000000 0000000000000000 000000007fe00000
>   GPR04 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR08 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR12 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR16 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR20 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR24 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   GPR28 0000000000000000 0000000000000000 0000000000000000 0000000000000000
>   CR 00000000  [ -  -  -  -  -  -  -  -  ]     RES 000@ffffffffffffffff
>    SRR0 0000000000000000  SRR1 0000000000000000    PVR 0000000000801200 VRSAVE 0000000000000000
>   SPRG0 0000000000000000 SPRG1 0000000000000000  SPRG2 0000000000000000  SPRG3 0000000000000000
>   SPRG4 0000000000000000 SPRG5 0000000000000000  SPRG6 0000000000000000  SPRG7 0000000000000000
>   HSRR0 0000000000000000 HSRR1 0000000000000000
>    CFAR 0000000000000000
>    LPCR 0000000000560413
>    PTCR 0000000000000000   DAR 0000000000000000  DSISR 0000000000000000
> 
> Fix this by adding the required support and handling in QEMU TCG L0.
> 
> [1] https://lore.kernel.org/all/20240605113913.83715-1-gautam@linux.ibm.com/
> 
> Fixes: 4a575f9a0567 ("spapr: nested: Initialize the GSB elements lookup table.")
> Suggested-by: Harsh Prateek Bora <harshpb@linux.ibm.com>
> Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com > ---
>   hw/ppc/spapr_nested.c         | 3 +++
>   include/hw/ppc/spapr_nested.h | 3 ++-
>   2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_nested.c b/hw/ppc/spapr_nested.c
> index c02785756c1e..b696ad537a77 100644
> --- a/hw/ppc/spapr_nested.c
> +++ b/hw/ppc/spapr_nested.c
> @@ -194,6 +194,7 @@ static void nested_save_state(struct nested_ppc_state *save, PowerPCCPU *cpu)
>           save->fscr = env->spr[SPR_FSCR];
>           save->pspb = env->spr[SPR_PSPB];
>           save->ctrl = env->spr[SPR_CTRL];
> +        save->dpdes = env->spr[SPR_DPDES];
>           save->vrsave = env->spr[SPR_VRSAVE];
>           save->dar = env->spr[SPR_DAR];
>           save->dsisr = env->spr[SPR_DSISR];
> @@ -293,6 +294,7 @@ static void nested_load_state(PowerPCCPU *cpu, struct nested_ppc_state *load)
>           env->spr[SPR_FSCR] = load->fscr;
>           env->spr[SPR_PSPB] = load->pspb;
>           env->spr[SPR_CTRL] = load->ctrl;
> +        env->spr[SPR_DPDES] = load->dpdes;
>           env->spr[SPR_VRSAVE] = load->vrsave;
>           env->spr[SPR_DAR] = load->dar;
>           env->spr[SPR_DSISR] = load->dsisr;
> @@ -982,6 +984,7 @@ struct guest_state_element_type guest_state_element_types[] = {
>       GUEST_STATE_ELEMENT_ENV_DW(GSB_VCPU_SPR_FSCR,  fscr),
>       GUEST_STATE_ELEMENT_ENV_W(GSB_VCPU_SPR_PSPB,   pspb),
>       GUEST_STATE_ELEMENT_ENV_DW(GSB_VCPU_SPR_CTRL,  ctrl),
> +    GUEST_STATE_ELEMENT_ENV_DW(GSB_VCPU_SPR_DPDES, dpdes),
>       GUEST_STATE_ELEMENT_ENV_W(GSB_VCPU_SPR_VRSAVE, vrsave),
>       GUEST_STATE_ELEMENT_ENV_DW(GSB_VCPU_SPR_DAR,   dar),
>       GUEST_STATE_ELEMENT_ENV_W(GSB_VCPU_SPR_DSISR,  dsisr),
> diff --git a/include/hw/ppc/spapr_nested.h b/include/hw/ppc/spapr_nested.h
> index 93ef14adcc5e..3b5cd993c256 100644
> --- a/include/hw/ppc/spapr_nested.h
> +++ b/include/hw/ppc/spapr_nested.h
> @@ -99,7 +99,8 @@
>   #define GSB_VCPU_SPR_HASHKEYR   0x1050
>   #define GSB_VCPU_SPR_HASHPKEYR  0x1051
>   #define GSB_VCPU_SPR_CTRL       0x1052
> -                    /* RESERVED 0x1053 - 0x1FFF */
> +#define GSB_VCPU_SPR_DPDES      0x1053
> +                    /* RESERVED 0x1054 - 0x1FFF */
>   #define GSB_VCPU_SPR_CR         0x2000
>   #define GSB_VCPU_SPR_PIDR       0x2001
>   #define GSB_VCPU_SPR_DSISR      0x2002
> 
> base-commit: aa54f5be44be786636a5d51cc1612ad208a24849