Re: [PATCH v7 3/6] mce: fix set_mce_nospec to always unmap the whole page

Borislav Petkov
2022-04-12T11:23:52Z

On Tue, Apr 05, 2022 at 01:47:44PM -0600, Jane Chu wrote:
> The set_memory_uc() approach doesn't work well in all cases.
> For example, when "The VMM unmapped the bad page from guest
> physical space and passed the machine check to the guest."
> "The guest gets virtual #MC on an access to that page.
> When the guest tries to do set_memory_uc() and instructs
> cpa_flush() to do clean caches that results in taking another
> fault / exception perhaps because the VMM unmapped the page
> from the guest."

I presume this is quoting someone...

> Since the driver has special knowledge to handle NP or UC,
> let's mark the poisoned page with NP and let driver handle it

s/let's mark/mark/

> when it comes down to repair.
>
> Please refer to discussions here for more details.
> https://lore.kernel.org/all/CAPcyv4hrXPb1tASBZUg-GgdVs0OOFKXMXLiHmktg_kFi7YBMyQ@mail.gmail.com/
>
> Now since poisoned page is marked as not-present, in order to
> avoid writing to a 'np' page and trigger kernel Oops, also fix

You can write it out: "non-present page..."

> pmem_do_write().
>
> Fixes: 284ce4011ba6 ("x86/memory_failure: Introduce {set, clear}_mce_nospec()")
> Signed-off-by: Jane Chu <jane.chu@oracle.com>
> ---
> arch/x86/kernel/cpu/mce/core.c | 6 +++---
> arch/x86/mm/pat/set_memory.c | 18 ++++++------------
> drivers/nvdimm/pmem.c | 31 +++++++------------------------
> include/linux/set_memory.h | 4 ++--
> 4 files changed, 18 insertions(+), 41 deletions(-)

For such mixed subsystem patches we probably should talk about who picks
them up, eventually...

> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 981496e6bc0e..fa67bb9d1afe 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -579,7 +579,7 @@ static int uc_decode_notifier(struct notifier_block *nb, unsigned long val,
>
> pfn = mce->addr >> PAGE_SHIFT;
> if (!memory_failure(pfn, 0)) {
> - set_mce_nospec(pfn, whole_page(mce));
> + set_mce_nospec(pfn);
> mce->kflags |= MCE_HANDLED_UC;
> }
>
> @@ -1316,7 +1316,7 @@ static void kill_me_maybe(struct callback_head *cb)
>
> ret = memory_failure(p->mce_addr >> PAGE_SHIFT, flags);
> if (!ret) {
> - set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
> + set_mce_nospec(p->mce_addr >> PAGE_SHIFT);
> sync_core();
> return;
> }
> @@ -1342,7 +1342,7 @@ static void kill_me_never(struct callback_head *cb)
> p->mce_count = 0;
> pr_err("Kernel accessed poison in user space at %llx\n", p->mce_addr);
> if (!memory_failure(p->mce_addr >> PAGE_SHIFT, 0))
> - set_mce_nospec(p->mce_addr >> PAGE_SHIFT, p->mce_whole_page);
> + set_mce_nospec(p->mce_addr >> PAGE_SHIFT);
> }

Both that ->mce_whole_page and whole_page() look unused after this.

--
Regards/Gruss,
Boris.