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Message-ID: <5e2336aa-90bf-b820-b5e4-e9a63088930f@csgroup.eu>
Date: Thu, 5 Aug 2021 12:06:15 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: sxwjean@...com, linuxppc-dev@...ts.ozlabs.org
Cc: oleg@...hat.com, mpe@...erman.id.au, benh@...nel.crashing.org,
paulus@...ba.org, ravi.bangoria@...ux.ibm.com, npiggin@...il.com,
aneesh.kumar@...ux.ibm.com, sandipan@...ux.ibm.com,
efremov@...ux.com, peterx@...hat.com, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org, Xiongwei Song <sxwjean@...il.com>
Subject: Re: [RFC PATCH 1/4] powerpc: Optimize register usage for esr register
Le 26/07/2021 à 16:30, sxwjean@...com a écrit :
> From: Xiongwei Song <sxwjean@...il.com>
>
> Create an anonymous union for dsisr and esr regsiters, we can reference
> esr to get the exception detail when CONFIG_4xx=y or CONFIG_BOOKE=y.
> Otherwise, reference dsisr. This makes code more clear.
I'm not sure it is worth doing that.
What is the point in doing the following when you know that regs->esr and regs->dsisr are exactly
the same:
> - err = ___do_page_fault(regs, regs->dar, regs->dsisr);
> + if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> + err = ___do_page_fault(regs, regs->dar, regs->esr);
> + else
> + err = ___do_page_fault(regs, regs->dar, regs->dsisr);
> +
Or even
> - int is_write = page_fault_is_write(regs->dsisr);
> + unsigned long err_reg;
> + int is_write;
> +
> + if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> + err_reg = regs->esr;
> + else
> + err_reg = regs->dsisr;
> +
> + is_write = page_fault_is_write(err_reg);
Artificially growing the code for that makes no sense to me.
To avoid anbiguity, maybe the best would be to rename regs->dsisr to something like regs->sr , so
that we know it represents the status register, which is DSISR or ESR depending on the platform.
>
> Signed-off-by: Xiongwei Song <sxwjean@...il.com>
> ---
> arch/powerpc/include/asm/ptrace.h | 5 ++++-
> arch/powerpc/include/uapi/asm/ptrace.h | 5 ++++-
> arch/powerpc/kernel/process.c | 2 +-
> arch/powerpc/kernel/ptrace/ptrace.c | 2 ++
> arch/powerpc/kernel/traps.c | 2 +-
> arch/powerpc/mm/fault.c | 16 ++++++++++++++--
> arch/powerpc/platforms/44x/machine_check.c | 4 ++--
> arch/powerpc/platforms/4xx/machine_check.c | 2 +-
> 8 files changed, 29 insertions(+), 9 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
> index 3e5d470a6155..c252d04b1206 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -44,7 +44,10 @@ struct pt_regs
> #endif
> unsigned long trap;
> unsigned long dar;
> - unsigned long dsisr;
> + union {
> + unsigned long dsisr;
> + unsigned long esr;
> + };
> unsigned long result;
> };
> };
> diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h
> index 7004cfea3f5f..e357288b5f34 100644
> --- a/arch/powerpc/include/uapi/asm/ptrace.h
> +++ b/arch/powerpc/include/uapi/asm/ptrace.h
> @@ -53,7 +53,10 @@ struct pt_regs
> /* N.B. for critical exceptions on 4xx, the dar and dsisr
> fields are overloaded to hold srr0 and srr1. */
> unsigned long dar; /* Fault registers */
> - unsigned long dsisr; /* on 4xx/Book-E used for ESR */
> + union {
> + unsigned long dsisr; /* on Book-S used for DSISR */
> + unsigned long esr; /* on 4xx/Book-E used for ESR */
> + };
> unsigned long result; /* Result of a system call */
> };
>
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 185beb290580..f74af8f9133c 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1499,7 +1499,7 @@ static void __show_regs(struct pt_regs *regs)
> trap == INTERRUPT_DATA_STORAGE ||
> trap == INTERRUPT_ALIGNMENT) {
> if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> - pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, regs->dsisr);
> + pr_cont("DEAR: "REG" ESR: "REG" ", regs->dar, regs->esr);
> else
> pr_cont("DAR: "REG" DSISR: %08lx ", regs->dar, regs->dsisr);
> }
> diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c
> index 0a0a33eb0d28..00789ad2c4a3 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace.c
> @@ -375,6 +375,8 @@ void __init pt_regs_check(void)
> offsetof(struct user_pt_regs, dar));
> BUILD_BUG_ON(offsetof(struct pt_regs, dsisr) !=
> offsetof(struct user_pt_regs, dsisr));
> + BUILD_BUG_ON(offsetof(struct pt_regs, esr) !=
> + offsetof(struct user_pt_regs, esr));
> BUILD_BUG_ON(offsetof(struct pt_regs, result) !=
> offsetof(struct user_pt_regs, result));
>
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index dfbce527c98e..2164f5705a0b 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -562,7 +562,7 @@ static inline int check_io_access(struct pt_regs *regs)
> #ifdef CONFIG_PPC_ADV_DEBUG_REGS
> /* On 4xx, the reason for the machine check or program exception
> is in the ESR. */
> -#define get_reason(regs) ((regs)->dsisr)
> +#define get_reason(regs) ((regs)->esr)
> #define REASON_FP ESR_FP
> #define REASON_ILLEGAL (ESR_PIL | ESR_PUO)
> #define REASON_PRIVILEGED ESR_PPR
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index a8d0ce85d39a..62953d4e7c93 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -541,7 +541,11 @@ static __always_inline void __do_page_fault(struct pt_regs *regs)
> {
> long err;
>
> - err = ___do_page_fault(regs, regs->dar, regs->dsisr);
> + if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> + err = ___do_page_fault(regs, regs->dar, regs->esr);
> + else
> + err = ___do_page_fault(regs, regs->dar, regs->dsisr);
> +
> if (unlikely(err))
> bad_page_fault(regs, err);
> }
> @@ -567,7 +571,15 @@ NOKPROBE_SYMBOL(hash__do_page_fault);
> */
> static void __bad_page_fault(struct pt_regs *regs, int sig)
> {
> - int is_write = page_fault_is_write(regs->dsisr);
> + unsigned long err_reg;
> + int is_write;
> +
> + if (IS_ENABLED(CONFIG_4xx) || IS_ENABLED(CONFIG_BOOKE))
> + err_reg = regs->esr;
> + else
> + err_reg = regs->dsisr;
> +
> + is_write = page_fault_is_write(err_reg);
>
> /* kernel has accessed a bad area */
>
> diff --git a/arch/powerpc/platforms/44x/machine_check.c b/arch/powerpc/platforms/44x/machine_check.c
> index a5c898bb9bab..5d19daacd78a 100644
> --- a/arch/powerpc/platforms/44x/machine_check.c
> +++ b/arch/powerpc/platforms/44x/machine_check.c
> @@ -11,7 +11,7 @@
>
> int machine_check_440A(struct pt_regs *regs)
> {
> - unsigned long reason = regs->dsisr;
> + unsigned long reason = regs->esr;
>
> printk("Machine check in kernel mode.\n");
> if (reason & ESR_IMCP){
> @@ -48,7 +48,7 @@ int machine_check_440A(struct pt_regs *regs)
> #ifdef CONFIG_PPC_47x
> int machine_check_47x(struct pt_regs *regs)
> {
> - unsigned long reason = regs->dsisr;
> + unsigned long reason = regs->esr;
> u32 mcsr;
>
> printk(KERN_ERR "Machine check in kernel mode.\n");
> diff --git a/arch/powerpc/platforms/4xx/machine_check.c b/arch/powerpc/platforms/4xx/machine_check.c
> index a71c29892a91..a905da1d6f41 100644
> --- a/arch/powerpc/platforms/4xx/machine_check.c
> +++ b/arch/powerpc/platforms/4xx/machine_check.c
> @@ -10,7 +10,7 @@
>
> int machine_check_4xx(struct pt_regs *regs)
> {
> - unsigned long reason = regs->dsisr;
> + unsigned long reason = regs->esr;
>
> if (reason & ESR_IMCP) {
> printk("Instruction");
>
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