Re: [PATCH] mm,hwpoison: return -EBUSY when page already poisoned

[Aili Yao <yaoaili@kingsoft.com>]

> As you answered in another email, p->mce_vaddr is set only on KERNEL_COPYIN case,
> then if p->mce_vaddr is available also for generic SRAR MCE (I'm assuming that we are
> talking about issues on race between generic SRAR MCE not only for KERNEL_COPYIN case),
> that might be helpful, although it might be hard to implement.
> And I'm afraid that walking page table could find the wrong virtual address if a process
> have multiple entries to the single page. We could send multiple SIGBUSs for such case,
> but maybe that's not an optimal solution.

Yes, agree, I can't find one way to address this multiple entries case, to make sure we get
the exact correct virtual address.

But also I will post a v2 RFC patch for this issue for only discussion purpose!

Thanks!

> ----
> From 147449a97e2ea3420ac3523f13523f5d30a13614 Mon Sep 17 00:00:00 2001
> From: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Date: Tue, 16 Mar 2021 14:22:21 +0900
> Subject: [PATCH] pagemap: expose hwpoison entry
> 
> not-signed-off-by-yet: Naoya Horiguchi <naoya.horiguchi@nec.com>
> ---
>  fs/proc/task_mmu.c      |  6 ++++++
>  include/linux/swapops.h | 12 ++++++++++++
>  tools/vm/page-types.c   |  5 ++++-
>  3 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 602e3a52884d..08cea209bae7 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -1300,6 +1300,7 @@ struct pagemapread {
>  #define PM_PFRAME_MASK		GENMASK_ULL(PM_PFRAME_BITS - 1, 0)
>  #define PM_SOFT_DIRTY		BIT_ULL(55)
>  #define PM_MMAP_EXCLUSIVE	BIT_ULL(56)
> +#define PM_HWPOISON	       	BIT_ULL(60)
>  #define PM_FILE			BIT_ULL(61)
>  #define PM_SWAP			BIT_ULL(62)
>  #define PM_PRESENT		BIT_ULL(63)
> @@ -1385,6 +1386,11 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
>  		if (is_migration_entry(entry))
>  			page = migration_entry_to_page(entry);
>  
> +		if (is_hwpoison_entry(entry)) {
> +			page = hwpoison_entry_to_page(entry);
> +			flags |= PM_HWPOISON;
> +		}
> +
>  		if (is_device_private_entry(entry))
>  			page = device_private_entry_to_page(entry);
>  	}
> diff --git a/include/linux/swapops.h b/include/linux/swapops.h
> index d9b7c9132c2f..1b9dedbd06ab 100644
> --- a/include/linux/swapops.h
> +++ b/include/linux/swapops.h
> @@ -323,6 +323,13 @@ static inline int is_hwpoison_entry(swp_entry_t entry)
>  	return swp_type(entry) == SWP_HWPOISON;
>  }
>  
> +static inline struct page *hwpoison_entry_to_page(swp_entry_t entry)
> +{
> +	struct page *p = pfn_to_page(swp_offset(entry));
> +	WARN_ON(!PageHWPoison(p));
> +	return p;
> +}
> +
>  static inline void num_poisoned_pages_inc(void)
>  {
>  	atomic_long_inc(&num_poisoned_pages);
> @@ -345,6 +352,11 @@ static inline int is_hwpoison_entry(swp_entry_t swp)
>  	return 0;
>  }
>  
> +static inline struct page *hwpoison_entry_to_page(swp_entry_t entry)
> +{
> +	return NULL;
> +}
> +
>  static inline void num_poisoned_pages_inc(void)
>  {
>  }
> diff --git a/tools/vm/page-types.c b/tools/vm/page-types.c
> index 0517c744b04e..1160d5a14955 100644
> --- a/tools/vm/page-types.c
> +++ b/tools/vm/page-types.c
> @@ -53,6 +53,7 @@
>  #define PM_SWAP_OFFSET(x)	(((x) & PM_PFRAME_MASK) >> MAX_SWAPFILES_SHIFT)
>  #define PM_SOFT_DIRTY		(1ULL << 55)
>  #define PM_MMAP_EXCLUSIVE	(1ULL << 56)
> +#define PM_HWPOISON		(1ULL << 60)
>  #define PM_FILE			(1ULL << 61)
>  #define PM_SWAP			(1ULL << 62)
>  #define PM_PRESENT		(1ULL << 63)
> @@ -311,6 +312,8 @@ static unsigned long pagemap_pfn(uint64_t val)
>  
>  	if (val & PM_PRESENT)
>  		pfn = PM_PFRAME(val);
> +	else if (val & PM_HWPOISON)
> +		pfn = PM_SWAP_OFFSET(val);
>  	else
>  		pfn = 0;
>  
> @@ -742,7 +745,7 @@ static void walk_vma(unsigned long index, unsigned long count)
>  			pfn = pagemap_pfn(buf[i]);
>  			if (pfn)
>  				walk_pfn(index + i, pfn, 1, buf[i]);
> -			if (buf[i] & PM_SWAP)
> +			else if (buf[i] & PM_SWAP)
>  				walk_swap(index + i, buf[i]);
>  		}
>  



-- 
Thanks!
Aili Yao