Re: [Qemu-devel] [Qemu-ppc] [PATCH v3 4/4] target-ppc: Handle ibm, nmi-register RTAS call

[Alexander Graf]

On 05.11.14 08:13, Aravinda Prasad wrote:
> This patch adds FWNMI support in qemu for powerKVM
> guests by handling the ibm,nmi-register rtas call.
> Whenever OS issues ibm,nmi-register RTAS call, the
> machine check notification address is saved and the
> machine check interrupt vector 0x200 is patched to
> issue a private hcall.
> 
> This patch also handles the cases when multi-processors
> experience machine check at or about the same time.
> As per PAPR, subsequent processors serialize waiting
> for the first processor to issue the ibm,nmi-interlock call.
> The second processor retries if the first processor which
> received a machine check is still reading the error log
> and is yet to issue ibm,nmi-interlock call.
> 
> Signed-off-by: Aravinda Prasad <address@hidden>
> ---
>  hw/ppc/spapr_hcall.c            |   16 +++++++
>  hw/ppc/spapr_rtas.c             |   93 
> +++++++++++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h          |   17 +++++++
>  pc-bios/spapr-rtas/spapr-rtas.S |   38 ++++++++++++++++
>  4 files changed, 163 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> index 8f16160..eceb5e5 100644
> --- a/hw/ppc/spapr_hcall.c
> +++ b/hw/ppc/spapr_hcall.c
> @@ -97,6 +97,9 @@ struct rtas_mc_log {
>      struct rtas_error_log err_log;
>  };
>  
> +/* Whether machine check handling is in progress by any CPU */
> +bool mc_in_progress;
> +
>  static void do_spr_sync(void *arg)
>  {
>      struct SPRSyncState *s = arg;
> @@ -678,6 +681,19 @@ static target_ulong h_report_mc_err(PowerPCCPU *cpu, 
> sPAPREnvironment *spapr,
>      cpu_synchronize_state(CPU(ppc_env_get_cpu(env)));
>  
>      /*
> +     * Only one VCPU can process machine check NMI at a time. Hence
> +     * set the lock mc_in_progress. Once the VCPU finishes processing
> +     * NMI, it executes ibm,nmi-interlock and mc_in_progress is unset
> +     * in ibm,nmi-interlock handler. Meanwhile if other VCPUs encounter
> +     * NMI we return 0 asking the VCPU to retry h_report_mc_err
> +     */
> +    if (mc_in_progress == 1) {

Please don't depend on bools being numbers. Use true / false. For if()s,
just don't use == at all - it makes it more readable.

> +        return 0;
> +    }
> +
> +    mc_in_progress = 1;
> +
> +    /*
>       * We save the original r3 register in SPRG2 in 0x200 vector,
>       * which is patched during call to ibm.nmi-register. Original
>       * r3 is required to be included in error log
> diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
> index 2ec2a8e..71c7662 100644
> --- a/hw/ppc/spapr_rtas.c
> +++ b/hw/ppc/spapr_rtas.c
> @@ -36,6 +36,9 @@
>  
>  #include <libfdt.h>
>  
> +#define BRANCH_INST_MASK  0xFC000000
> +extern bool mc_in_progress;

Please put this into the spapr struct.

> +
>  static void rtas_display_character(PowerPCCPU *cpu, sPAPREnvironment *spapr,
>                                     uint32_t token, uint32_t nargs,
>                                     target_ulong args,
> @@ -290,6 +293,90 @@ static void rtas_ibm_os_term(PowerPCCPU *cpu,
>      rtas_st(rets, 0, ret);
>  }
>  
> +static void rtas_ibm_nmi_register(PowerPCCPU *cpu,
> +                                  sPAPREnvironment *spapr,
> +                                  uint32_t token, uint32_t nargs,
> +                                  target_ulong args,
> +                                  uint32_t nret, target_ulong rets)
> +{
> +    int i;
> +    uint32_t ori_inst = 0x60630000;
> +    uint32_t branch_inst = 0x48000002;
> +    target_ulong guest_machine_check_addr;
> +    uint32_t trampoline[TRAMPOLINE_INSTS];
> +    int total_inst = sizeof(trampoline) / sizeof(uint32_t);

ARRAY_SIZE(trampoline), though I don't quite understand why you need a
variable that contains the same value as a constant (TRAMPOLINE_INSTS).

But since you're moving all of those bits into variable fields on the
rtas blob itself as we discussed in the last version, I guess this code
will go away anyways ;).

> +    PowerPCCPUClass *pcc = POWERPC_CPU_GET_CLASS(cpu);
> +
> +    /* Store the system reset and machine check address */
> +    guest_machine_check_addr = rtas_ld(args, 1);

Load or Store? I don't find the comment particularly useful either ;).

> +
> +    /*
> +     * Read the trampoline instructions from RTAS Blob and patch
> +     * the KVMPPC_H_REPORT_MC_ERR hcall number and the guest
> +     * machine check address before copying to 0x200 vector
> +     */
> +    cpu_physical_memory_read(spapr->rtas_addr + RTAS_TRAMPOLINE_OFFSET,
> +                             trampoline, sizeof(trampoline));
> +
> +    /* Safety Check */

Same for this comment.

> +    QEMU_BUILD_BUG_ON(sizeof(trampoline) > MC_INTERRUPT_VECTOR_SIZE);
> +
> +    /* Update the KVMPPC_H_REPORT_MC_ERR value in trampoline */
> +    ori_inst |= KVMPPC_H_REPORT_MC_ERR;
> +    memcpy(&trampoline[TRAMPOLINE_ORI_INST_INDEX], &ori_inst,
> +            sizeof(ori_inst));

Why memcpy a u32 into a u32 array?

> +
> +    /*
> +     * Sanity check guest_machine_check_addr to prevent clobbering
> +     * operator value in branch instruction
> +     */
> +    if (guest_machine_check_addr & BRANCH_INST_MASK) {
> +        fprintf(stderr, "Unable to register ibm,nmi_register: "
> +                "Invalid machine check handler address\n");

In general, printf's in guest triggerable code aren't a great idea,
since the guest could flood our host logs with this. I can't say we're
doing a great job at it already though, so it probably doesn't matter much.

> +        rtas_st(rets, 0, RTAS_OUT_NOT_SUPPORTED);
> +        return;
> +    }
> +
> +    /*
> +     * Update the branch instruction in trampoline
> +     * with the absolute machine check address requested by OS.
> +     */
> +    branch_inst |= guest_machine_check_addr;
> +    memcpy(&trampoline[TRAMPOLINE_BR_INST_INDEX], &branch_inst,
> +            sizeof(branch_inst));
> +
> +    /* Handle all Host/Guest LE/BE combinations */
> +    if ((*pcc->interrupts_big_endian)(cpu)) {
> +        for (i = 0; i < total_inst; i++) {
> +            trampoline[i] = cpu_to_be32(trampoline[i]);
> +        }
> +    } else {
> +        for (i = 0; i < total_inst; i++) {
> +            trampoline[i] = cpu_to_le32(trampoline[i]);
> +        }
> +    }
> +
> +    /* Patch 0x200 NMI interrupt vector memory area of guest */
> +    cpu_physical_memory_write(MC_INTERRUPT_VECTOR, trampoline,
> +                              sizeof(trampoline));
> +
> +    rtas_st(rets, 0, RTAS_OUT_SUCCESS);
> +}
> +
> +static void rtas_ibm_nmi_interlock(PowerPCCPU *cpu,
> +                                   sPAPREnvironment *spapr,
> +                                   uint32_t token, uint32_t nargs,
> +                                   target_ulong args,
> +                                   uint32_t nret, target_ulong rets)
> +{
> +    /*
> +     * VCPU issuing ibm,nmi-interlock is done with NMI handling,
> +     * hence unset mc_in_progress.
> +     */
> +    mc_in_progress = 0;
> +    rtas_st(rets, 0, RTAS_OUT_SUCCESS);
> +}
> +
>  static struct rtas_call {
>      const char *name;
>      spapr_rtas_fn fn;
> @@ -419,6 +506,12 @@ static void core_rtas_register_types(void)
>                          rtas_ibm_set_system_parameter);
>      spapr_rtas_register(RTAS_IBM_OS_TERM, "ibm,os-term",
>                          rtas_ibm_os_term);
> +    spapr_rtas_register(RTAS_IBM_NMI_REGISTER,
> +                        "ibm,nmi-register",
> +                        rtas_ibm_nmi_register);
> +    spapr_rtas_register(RTAS_IBM_NMI_INTERLOCK,
> +                        "ibm,nmi-interlock",
> +                        rtas_ibm_nmi_interlock);
>  }
>  
>  type_init(core_rtas_register_types)
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index a2d67e9..98d0a6c 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -384,8 +384,10 @@ int spapr_allocate_irq_block(int num, bool lsi, bool 
> msi);
>  #define RTAS_GET_SENSOR_STATE                   (RTAS_TOKEN_BASE + 0x1D)
>  #define RTAS_IBM_CONFIGURE_CONNECTOR            (RTAS_TOKEN_BASE + 0x1E)
>  #define RTAS_IBM_OS_TERM                        (RTAS_TOKEN_BASE + 0x1F)
> +#define RTAS_IBM_NMI_REGISTER                   (RTAS_TOKEN_BASE + 0x20)
> +#define RTAS_IBM_NMI_INTERLOCK                  (RTAS_TOKEN_BASE + 0x21)
>  
> -#define RTAS_TOKEN_MAX                          (RTAS_TOKEN_BASE + 0x20)
> +#define RTAS_TOKEN_MAX                          (RTAS_TOKEN_BASE + 0x22)
>  
>  /* RTAS ibm,get-system-parameter token values */
>  #define RTAS_SYSPARM_SPLPAR_CHARACTERISTICS      20
> @@ -488,4 +490,17 @@ int spapr_tcet_dma_dt(void *fdt, int node_off, const 
> char *propname,
>  #define RTAS_TRAMPOLINE_OFFSET   0x200
>  #define RTAS_ERRLOG_OFFSET       0x800
>  
> +/* Machine Check Trampoline related macros
> + *
> + * These macros should co-relate to the code we
> + * have in pc-bios/spapr-rtas/spapr-rtas.S
> + */
> +#define TRAMPOLINE_INSTS           17
> +#define TRAMPOLINE_ORI_INST_INDEX  2
> +#define TRAMPOLINE_BR_INST_INDEX   15
> +
> +/* Machine Check Interrupt related macros */
> +#define MC_INTERRUPT_VECTOR           0x200
> +#define MC_INTERRUPT_VECTOR_SIZE      0x100
> +
>  #endif /* !defined (__HW_SPAPR_H__) */
> diff --git a/pc-bios/spapr-rtas/spapr-rtas.S b/pc-bios/spapr-rtas/spapr-rtas.S
> index 903bec2..c315332 100644
> --- a/pc-bios/spapr-rtas/spapr-rtas.S
> +++ b/pc-bios/spapr-rtas/spapr-rtas.S

Please add #defines at the top of the file for the register names:

  #define r0 0
  #define r1 1
  ...

That way the code below will get much more readable :)

Also, you want a jump table here as we discussed in the last review
round. That table would tell you

  a) Entry address for RTAS
  b) Offset of the NMI code
  c) To-be-patched offsets of the instructions inside the NMI code

Then we have all offsets automatically generated inside a single file
and don't have to maintain fragile relationships between random headers
with offset defines and the .S file.


Alex

> @@ -35,3 +35,41 @@ _start:
>       ori     3,3,address@hidden
>       sc      1
>       blr
> +     . = 0x200
> +     /*
> +      * Trampoline saves r3 in sprg2 and issues private hcall
> +      * to request qemu to build error log. QEMU builds the
> +      * error log, copies to rtas-blob and returns the address.
> +      * The initial 16 bytes in return adress consist of saved
> +      * srr0 and srr1 which we restore and pass on the actual error
> +      * log address to OS handled mcachine check notification
> +      * routine
> +      *
> +      * All the below instructions are copied to interrupt vector
> +      * 0x200 at the time of handling ibm,nmi-register rtas call.
> +      */
> +     mtsprg  2,3
> +     li      3,0
> +     /*
> +      * ori r3,r3,KVMPPC_H_REPORT_MC_ERR. The KVMPPC_H_REPORT_MC_ERR
> +      * value is patched below
> +      */
> +1:   ori     3,3,0
> +     sc      1               /* Issue H_CALL */
> +     cmpdi   cr0,3,0
> +     beq     cr0,1b          /* retry KVMPPC_H_REPORT_MC_ERR */
> +     mtsprg  2,4
> +     ld      4,0(3)
> +     mtsrr0  4               /* Restore srr0 */
> +     ld      4,8(3)
> +     mtsrr1  4               /* Restore srr1 */
> +     ld      4,16(3)
> +     mtcrf   0,4             /* Restore cr */
> +     addi    3,3,24
> +     mfsprg  4,2
> +     /*
> +      * Branch to address registered by OS. The branch address is
> +      * patched in the ibm,nmi-register rtas call.
> +      */
> +     ba      0x0
> +     b       .
> 
>