linux-kernel - Re: [RFC v5 32/38] powerpc: capture the violated protection key on fault

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Message-Id: <5fa43f48-d3b3-89f2-0bbd-58be3e07f4b8@linux.vnet.ibm.com>
Date:   Mon, 10 Jul 2017 08:40:19 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, dave.hansen@...el.com, hbabu@...ibm.com,
        arnd@...db.de, akpm@...ux-foundation.org, corbet@....net,
        mingo@...hat.com
Subject: Re: [RFC v5 32/38] powerpc: capture the violated protection key on
 fault

On 07/06/2017 02:52 AM, Ram Pai wrote:
> Capture the protection key that got violated in paca.
> This value will be used by used to inform the signal
> handler.
> 
> Signed-off-by: Ram Pai <linuxram@...ibm.com>
> ---
>  arch/powerpc/include/asm/paca.h   |    1 +
>  arch/powerpc/kernel/asm-offsets.c |    1 +
>  arch/powerpc/mm/fault.c           |    3 +++
>  3 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
> index c8bd1fc..0c06188 100644
> --- a/arch/powerpc/include/asm/paca.h
> +++ b/arch/powerpc/include/asm/paca.h
> @@ -94,6 +94,7 @@ struct paca_struct {
>  	u64 dscr_default;		/* per-CPU default DSCR */
>  #ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>  	u64 paca_amr;			/* value of amr at exception */
> +	u16 paca_pkey;                  /* exception causing pkey */
>  #endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
>  
>  #ifdef CONFIG_PPC_STD_MMU_64
> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
> index 17f5d8a..7dff862 100644
> --- a/arch/powerpc/kernel/asm-offsets.c
> +++ b/arch/powerpc/kernel/asm-offsets.c
> @@ -244,6 +244,7 @@ int main(void)
>  
>  #ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>  	OFFSET(PACA_AMR, paca_struct, paca_amr);
> +	OFFSET(PACA_PKEY, paca_struct, paca_pkey);
>  #endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
>  
>  	OFFSET(ACCOUNT_STARTTIME, paca_struct, accounting.starttime);
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index a6710f5..c8674a7 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -265,6 +265,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  	if (error_code & DSISR_KEYFAULT) {
>  		code = SEGV_PKUERR;
>  		get_paca()->paca_amr = read_amr();
> +		get_paca()->paca_pkey = get_pte_pkey(current->mm, address);
>  		goto bad_area_nosemaphore;
>  	}
>  #endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> @@ -290,6 +291,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  
>  	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
>  
> +

Stray empty line addition here.

>  	/*
>  	 * We want to do this outside mmap_sem, because reading code around nip
>  	 * can result in fault, which will cause a deadlock when called with
> @@ -453,6 +455,7 @@ int do_page_fault(struct pt_regs *regs, unsigned long address,
>  	if (!arch_vma_access_permitted(vma, flags & FAULT_FLAG_WRITE,
>  			is_exec, 0)) {
>  		get_paca()->paca_amr = read_amr();
> +		get_paca()->paca_pkey = vma_pkey(vma);

Why not get_pte_pkey() here as well ? IIUC both these function would
give us the same pkey, then why is the difference when we process a
page fault for real protection key violation in HW compared to cross
checking of VMA protection key in SW for regular page faults.