linux-kernel - Re: [PATCH v10 2/7] powerpc/mce: Fix MCE handling for huge pages

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Message-Id: <1566223931.kpuwkor3n7.astroid@bobo.none>
Date:   Tue, 20 Aug 2019 00:22:35 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Linux Kernel <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Santosh Sivaraj <santosh@...six.org>
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Reza Arbab <arbab@...ux.ibm.com>,
        Balbir Singh <bsingharora@...il.com>,
        Chandan Rajendra <chandan@...ux.ibm.com>,
        christophe leroy <christophe.leroy@....fr>,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Michael Ellerman <mpe@...erman.id.au>, stable@...r.kernel.org
Subject: Re: [PATCH v10 2/7] powerpc/mce: Fix MCE handling for huge pages

Santosh Sivaraj's on August 15, 2019 10:39 am:
> From: Balbir Singh <bsingharora@...il.com>
> 
> The current code would fail on huge pages addresses, since the shift would
> be incorrect. Use the correct page shift value returned by
> __find_linux_pte() to get the correct physical address. The code is more
> generic and can handle both regular and compound pages.
> 
> Fixes: ba41e1e1ccb9 ("powerpc/mce: Hookup derror (load/store) UE errors")
> Signed-off-by: Balbir Singh <bsingharora@...il.com>
> [arbab@...ux.ibm.com: Fixup pseries_do_memory_failure()]
> Signed-off-by: Reza Arbab <arbab@...ux.ibm.com>
> Co-developed-by: Santosh Sivaraj <santosh@...six.org>
> Signed-off-by: Santosh Sivaraj <santosh@...six.org>
> Tested-by: Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>
> Cc: stable@...r.kernel.org # v4.15+
> ---
>  arch/powerpc/include/asm/mce.h       |  2 +-
>  arch/powerpc/kernel/mce_power.c      | 55 ++++++++++++++--------------
>  arch/powerpc/platforms/pseries/ras.c |  9 ++---
>  3 files changed, 32 insertions(+), 34 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/mce.h b/arch/powerpc/include/asm/mce.h
> index a4c6a74ad2fb..f3a6036b6bc0 100644
> --- a/arch/powerpc/include/asm/mce.h
> +++ b/arch/powerpc/include/asm/mce.h
> @@ -209,7 +209,7 @@ extern void release_mce_event(void);
>  extern void machine_check_queue_event(void);
>  extern void machine_check_print_event_info(struct machine_check_event *evt,
>  					   bool user_mode, bool in_guest);
> -unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr);
> +unsigned long addr_to_phys(struct pt_regs *regs, unsigned long addr);
>  #ifdef CONFIG_PPC_BOOK3S_64
>  void flush_and_reload_slb(void);
>  #endif /* CONFIG_PPC_BOOK3S_64 */
> diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
> index a814d2dfb5b0..e74816f045f8 100644
> --- a/arch/powerpc/kernel/mce_power.c
> +++ b/arch/powerpc/kernel/mce_power.c
> @@ -20,13 +20,14 @@
>  #include <asm/exception-64s.h>
>  
>  /*
> - * Convert an address related to an mm to a PFN. NOTE: we are in real
> - * mode, we could potentially race with page table updates.
> + * Convert an address related to an mm to a physical address.
> + * NOTE: we are in real mode, we could potentially race with page table updates.
>   */
> -unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
> +unsigned long addr_to_phys(struct pt_regs *regs, unsigned long addr)
>  {
> -	pte_t *ptep;
> -	unsigned long flags;
> +	pte_t *ptep, pte;
> +	unsigned int shift;
> +	unsigned long flags, phys_addr;
>  	struct mm_struct *mm;
>  
>  	if (user_mode(regs))
> @@ -35,14 +36,21 @@ unsigned long addr_to_pfn(struct pt_regs *regs, unsigned long addr)
>  		mm = &init_mm;
>  
>  	local_irq_save(flags);
> -	if (mm == current->mm)
> -		ptep = find_current_mm_pte(mm->pgd, addr, NULL, NULL);
> -	else
> -		ptep = find_init_mm_pte(addr, NULL);
> +	ptep = __find_linux_pte(mm->pgd, addr, NULL, &shift);
>  	local_irq_restore(flags);
> +
>  	if (!ptep || pte_special(*ptep))
>  		return ULONG_MAX;
> -	return pte_pfn(*ptep);
> +
> +	pte = *ptep;
> +	if (shift > PAGE_SHIFT) {
> +		unsigned long rpnmask = (1ul << shift) - PAGE_SIZE;
> +
> +		pte = __pte(pte_val(pte) | (addr & rpnmask));
> +	}
> +	phys_addr = pte_pfn(pte) << PAGE_SHIFT;
> +
> +	return phys_addr;
>  }

This should remain addr_to_pfn I think. None of the callers care what
size page the EA was mapped with. 'pfn' is referring to the Linux pfn,
which is the small page number.

  if (shift > PAGE_SHIFT)
    return (pte_pfn(*ptep) | ((addr & ((1UL << shift) - 1)) >> PAGE_SHIFT);
  else
    return pte_pfn(*ptep);

Something roughly like that, then you don't have to change any callers
or am I missing something?

Thanks,
Nick