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Date: Sat, 16 May 2020 17:36:33 +1000
From: Nicholas Piggin <npiggin@...il.com>
To: Allison Randal <allison@...utok.net>,
Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Daniel Axtens <dja@...ens.net>,
"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
Leonardo Bras <leobras.c@...il.com>,
Michael Ellerman <mpe@...erman.id.au>,
Nadav Amit <namit@...are.com>,
Nathan Lynch <nathanl@...ux.ibm.com>,
Paul Mackerras <paulus@...ba.org>,
Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v5 2/2] powerpc/rtas: Implement reentrant rtas call
Excerpts from Leonardo Bras's message of May 16, 2020 3:21 pm:
> Implement rtas_call_reentrant() for reentrant rtas-calls:
> "ibm,int-on", "ibm,int-off",ibm,get-xive" and "ibm,set-xive".
>
> On LoPAPR Version 1.1 (March 24, 2016), from 7.3.10.1 to 7.3.10.4,
> items 2 and 3 say:
>
> 2 - For the PowerPC External Interrupt option: The * call must be
> reentrant to the number of processors on the platform.
> 3 - For the PowerPC External Interrupt option: The * argument call
> buffer for each simultaneous call must be physically unique.
>
> So, these rtas-calls can be called in a lockless way, if using
> a different buffer for each cpu doing such rtas call.
>
> For this, it was suggested to add the buffer (struct rtas_args)
> in the PACA struct, so each cpu can have it's own buffer.
> The PACA struct received a pointer to rtas buffer, which is
> allocated in the memory range available to rtas 32-bit.
>
> Reentrant rtas calls are useful to avoid deadlocks in crashing,
> where rtas-calls are needed, but some other thread crashed holding
> the rtas.lock.
>
> This is a backtrace of a deadlock from a kdump testing environment:
>
> #0 arch_spin_lock
> #1 lock_rtas ()
> #2 rtas_call (token=8204, nargs=1, nret=1, outputs=0x0)
> #3 ics_rtas_mask_real_irq (hw_irq=4100)
> #4 machine_kexec_mask_interrupts
> #5 default_machine_crash_shutdown
> #6 machine_crash_shutdown
> #7 __crash_kexec
> #8 crash_kexec
> #9 oops_end
>
> Signed-off-by: Leonardo Bras <leobras.c@...il.com>
> ---
> arch/powerpc/include/asm/paca.h | 2 ++
> arch/powerpc/include/asm/rtas.h | 1 +
> arch/powerpc/kernel/paca.c | 20 +++++++++++
> arch/powerpc/kernel/rtas.c | 52 +++++++++++++++++++++++++++++
> arch/powerpc/sysdev/xics/ics-rtas.c | 22 ++++++------
> 5 files changed, 86 insertions(+), 11 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index e3cc9eb9204d..87cd9c2220cc 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -29,6 +29,7 @@
> #include <asm/hmi.h>
> #include <asm/cpuidle.h>
> #include <asm/atomic.h>
> +#include <asm/rtas-types.h>
>
> #include <asm-generic/mmiowb_types.h>
>
> @@ -270,6 +271,7 @@ struct paca_struct {
> #ifdef CONFIG_MMIOWB
> struct mmiowb_state mmiowb_state;
> #endif
> + struct rtas_args *reentrant_args;
> } ____cacheline_aligned;
>
> extern void copy_mm_to_paca(struct mm_struct *mm);
> diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
> index c35c5350b7e4..fa7509c85881 100644
> --- a/arch/powerpc/include/asm/rtas.h
> +++ b/arch/powerpc/include/asm/rtas.h
> @@ -236,6 +236,7 @@ extern struct rtas_t rtas;
> extern int rtas_token(const char *service);
> extern int rtas_service_present(const char *service);
> extern int rtas_call(int token, int, int, int *, ...);
> +int rtas_call_reentrant(int token, int nargs, int nret, int *outputs, ...);
> void rtas_call_unlocked(struct rtas_args *args, int token, int nargs,
> int nret, ...);
> extern void __noreturn rtas_restart(char *cmd);
> diff --git a/arch/powerpc/kernel/paca.c b/arch/powerpc/kernel/paca.c
> index 3f91ccaa9c74..88c9b61489fc 100644
> --- a/arch/powerpc/kernel/paca.c
> +++ b/arch/powerpc/kernel/paca.c
> @@ -16,6 +16,7 @@
> #include <asm/kexec.h>
> #include <asm/svm.h>
> #include <asm/ultravisor.h>
> +#include <asm/rtas.h>
>
> #include "setup.h"
>
> @@ -164,6 +165,23 @@ static struct slb_shadow * __init new_slb_shadow(int cpu, unsigned long limit)
>
> #endif /* CONFIG_PPC_BOOK3S_64 */
>
> +/**
> + * new_rtas_args() - Allocates rtas args
> + * @cpu: CPU number
> + * @limit: Memory limit for this allocation
> + *
> + * Allocates a struct rtas_args and return it's pointer.
> + *
> + * Return: Pointer to allocated rtas_args
> + */
> +static struct rtas_args * __init new_rtas_args(int cpu, unsigned long limit)
> +{
> + limit = min_t(unsigned long, limit, RTAS_INSTANTIATE_MAX);
> +
> + return alloc_paca_data(sizeof(struct rtas_args), L1_CACHE_BYTES,
> + limit, cpu);
> +}
> +
> /* The Paca is an array with one entry per processor. Each contains an
> * lppaca, which contains the information shared between the
> * hypervisor and Linux.
> @@ -202,6 +220,7 @@ void __init __nostackprotector initialise_paca(struct paca_struct *new_paca, int
> /* For now -- if we have threads this will be adjusted later */
> new_paca->tcd_ptr = &new_paca->tcd;
> #endif
> + new_paca->reentrant_args = NULL;
> }
>
> /* Put the paca pointer into r13 and SPRG_PACA */
> @@ -274,6 +293,7 @@ void __init allocate_paca(int cpu)
> #ifdef CONFIG_PPC_BOOK3S_64
> paca->slb_shadow_ptr = new_slb_shadow(cpu, limit);
> #endif
> + paca->reentrant_args = new_rtas_args(cpu, limit);
Good, I think tihs should work as you want now. Can you allocate it like
lppacas? Put it under PSERIES (and in the paca) and check for !HV?
Thanks,
Nick
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