Re: [PATCH v2] spapr: nested: Add support for DPDES SPR in GSB for TCG L0

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

On 10/18/24 22:08, 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 (Guest State
> Buffer) element for DPDES was added in Linux; the same has been missing
> in TCG L0 implementation. Add 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
> following crash. The crash occurs while handling the GUEST_RUN_VCPU
> hcall made in TCG L0. In the hcall handling path, map_and_getset_state()
> calls getset_state(), which, in turn, calls guest_state_request_check()
> to validate the GSR (Guest State Request) elements. During this process,
> guest_state_request_check() iterates over the GSR elements and receives
> a NULL return code from guest_state_element_type_find() for the type
> variable corresponding to the DPDES register's elemetn ID (which was
> unknown to TCG L0). Subsequently, getset_state() returns H_P3,
> ultimately leading to the hcall failure and causing the KVM guest to
> crash.
> 
>   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 in TCG L0 implementation of
> APIv2.
> 
> [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>
> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>

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

> ---
> Changes since v1:
>      - Addressed Harsh's comments on v1
>      - Updated the patch description to more precise details of the issue
>      - v1: https://lore.kernel.org/all/20241017110033.3929988-1-amachhiw@linux.ibm.com/
> 
>   hw/ppc/spapr_nested.c         | 1 +
>   include/hw/ppc/spapr_nested.h | 3 ++-
>   2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_nested.c b/hw/ppc/spapr_nested.c
> index c02785756c1e..1b41c8fb8b67 100644
> --- a/hw/ppc/spapr_nested.c
> +++ b/hw/ppc/spapr_nested.c
> @@ -982,6 +982,7 @@ 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