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Date: Mon, 30 May 2022 05:02:34 +0000
From: HORIGUCHI NAOYA(堀口 直也)
<naoya.horiguchi@....com>
To: zhenwei pi <pizhenwei@...edance.com>
CC: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"mst@...hat.com" <mst@...hat.com>,
"david@...hat.com" <david@...hat.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"jasowang@...hat.com" <jasowang@...hat.com>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"peterx@...hat.com" <peterx@...hat.com>,
"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>
Subject: Re: [PATCH 2/3] mm/memory-failure.c: support reset PTE during
unpoison
On Fri, May 20, 2022 at 03:06:47PM +0800, zhenwei pi wrote:
> Origianlly, unpoison_memory() is only used by hwpoison-inject, and
> unpoisons a page which is poisoned by hwpoison-inject too. The kernel PTE
> entry has no change during software poison/unpoison.
>
> On a virtualization platform, it's possible to fix hardware corrupted page
> by hypervisor, typically the hypervisor remaps the error HVA(host virtual
> address). So add a new parameter 'const char *reason' to show the reason
> called by.
>
> Once the corrupted page gets fixed, the guest kernel needs put page to
> buddy. Reuse the page and hit the following issue(Intel Platinum 8260):
> BUG: unable to handle page fault for address: ffff888061646000
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD 2c01067 P4D 2c01067 PUD 61aaa063 PMD 10089b063 PTE 800fffff9e9b9062
> Oops: 0002 [#1] PREEMPT SMP NOPTI
> CPU: 2 PID: 31106 Comm: stress Kdump: loaded Tainted: G M OE 5.18.0-rc6.bm.1-amd64 #6
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> RIP: 0010:clear_page_erms+0x7/0x10
>
> The kernel PTE entry of the fixed page is still uncorrected, kernel hits
> page fault during prep_new_page. So add 'bool reset_kpte' to get a change
> to fix the PTE entry if the page is fixed by hypervisor.
>
> Signed-off-by: zhenwei pi <pizhenwei@...edance.com>
> ---
> include/linux/mm.h | 2 +-
> mm/hwpoison-inject.c | 2 +-
> mm/memory-failure.c | 26 +++++++++++++++++++-------
> 3 files changed, 21 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 665873c2788c..7ba210e86401 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3191,7 +3191,7 @@ enum mf_flags {
> extern int memory_failure(unsigned long pfn, int flags);
> extern void memory_failure_queue(unsigned long pfn, int flags);
> extern void memory_failure_queue_kick(int cpu);
> -extern int unpoison_memory(unsigned long pfn);
> +extern int unpoison_memory(unsigned long pfn, bool reset_kpte, const char *reason);
> extern int sysctl_memory_failure_early_kill;
> extern int sysctl_memory_failure_recovery;
> extern void shake_page(struct page *p);
> diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
> index 5c0cddd81505..0dd17ba98ade 100644
> --- a/mm/hwpoison-inject.c
> +++ b/mm/hwpoison-inject.c
> @@ -57,7 +57,7 @@ static int hwpoison_unpoison(void *data, u64 val)
> if (!capable(CAP_SYS_ADMIN))
> return -EPERM;
>
> - return unpoison_memory(val);
> + return unpoison_memory(val, false, "hwpoison-inject");
> }
>
> DEFINE_DEBUGFS_ATTRIBUTE(hwpoison_fops, NULL, hwpoison_inject, "%lli\n");
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 95c218bb0a37..a46de3be1dd7 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2132,21 +2132,26 @@ core_initcall(memory_failure_init);
> /**
> * unpoison_memory - Unpoison a previously poisoned page
> * @pfn: Page number of the to be unpoisoned page
> + * @reset_kpte: Reset the PTE entry for kmap
> + * @reason: The callers tells why unpoisoning the page
> *
> - * Software-unpoison a page that has been poisoned by
> - * memory_failure() earlier.
> + * Unpoison a page that has been poisoned by memory_failure() earlier.
> *
> - * This is only done on the software-level, so it only works
> - * for linux injected failures, not real hardware failures
> + * For linux injected failures, there is no need to reset PTE entry.
> + * It's possible to fix hardware memory failure on a virtualization platform,
> + * once hypervisor fixes the failure, guest needs put page back to buddy and
> + * reset the PTE entry in kernel.
> *
> * Returns 0 for success, otherwise -errno.
> */
> -int unpoison_memory(unsigned long pfn)
> +int unpoison_memory(unsigned long pfn, bool reset_kpte, const char *reason)
> {
> struct page *page;
> struct page *p;
> int ret = -EBUSY;
> int freeit = 0;
> + pte_t *kpte;
> + unsigned long addr;
These variables are used only in "if (reset_kpte)" block, so you can
move the definitions in it.
> static DEFINE_RATELIMIT_STATE(unpoison_rs, DEFAULT_RATELIMIT_INTERVAL,
> DEFAULT_RATELIMIT_BURST);
>
> @@ -2208,8 +2213,15 @@ int unpoison_memory(unsigned long pfn)
> mutex_unlock(&mf_mutex);
> if (!ret || freeit) {
> num_poisoned_pages_dec();
> - unpoison_pr_info("Unpoison: Software-unpoisoned page %#lx\n",
> - page_to_pfn(p), &unpoison_rs);
> + pr_info("Unpoison: Unpoisoned page %#lx by %s\n",
> + page_to_pfn(p), reason);
Do you need undoing rate limiting here? In the original unpoison's usage,
avoiding flood of "Unpoison: Software-unpoisoned page" messages is helpful.
And unpoison seems to be called from virtio-balloon multiple times when
the backend is 2MB hugepages. If it's right, printing out 512 lines of
"Unpoison: Unpoisoned page 0xXXX by virtio-balloon" messages might not be
so helpful?
Thanks,
Naoya Horiguchi
> + if (reset_kpte) {
> + preempt_disable();
> + addr = (unsigned long)page_to_virt(p);
> + kpte = virt_to_kpte(addr);
> + set_pte_at(&init_mm, addr, kpte, pfn_pte(pfn, PAGE_KERNEL));
> + preempt_enable();
> + }
> }
> return ret;
> }
> --
> 2.20.1
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