2023-11-23 00:37:06

by Ankit Agrawal

Subject: [PATCH v2 2/4] mm: Add poison error check in fixup_user_fault() for mapped pfn

From: Ankit Agrawal <[email protected]>

The fixup_user_fault() currently does not expect a VM_FAULT_HWPOISON
and hence does not check for it while calling vm_fault_to_errno(). Since
we now have a new code path which can trigger such case, change
fixup_user_fault to look for VM_FAULT_HWPOISON.

Also make hva_to_pfn_remapped check for -EHWPOISON and communicate the
poison fault up to the user_mem_abort().

Signed-off-by: Ankit Agrawal <[email protected]>
---
mm/gup.c | 2 +-
virt/kvm/kvm_main.c | 6 ++++++
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index 231711efa390..b78af20a0f52 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1414,7 +1414,7 @@ int fixup_user_fault(struct mm_struct *mm,
}

if (ret & VM_FAULT_ERROR) {
- int err = vm_fault_to_errno(ret, 0);
+ int err = vm_fault_to_errno(ret, FOLL_HWPOISON);

if (err)
return err;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 486800a7024b..2ff067f21a7c 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2731,6 +2731,12 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool interruptible,
r = hva_to_pfn_remapped(vma, addr, write_fault, writable, &pfn);
if (r == -EAGAIN)
goto retry;
+
+ if (r == -EHWPOISON) {
+ pfn = KVM_PFN_ERR_HWPOISON;
+ goto exit;
+ }
+
if (r < 0)
pfn = KVM_PFN_ERR_FAULT;
} else {
--
2.17.1

2023-12-01 17:05:35

by Sean Christopherson

Subject: Re: [PATCH v2 2/4] mm: Add poison error check in fixup_user_fault() for mapped pfn

On Thu, Nov 23, 2023, [email protected] wrote:
> From: Ankit Agrawal <[email protected]>
>
> The fixup_user_fault() currently does not expect a VM_FAULT_HWPOISON
> and hence does not check for it while calling vm_fault_to_errno(). Since
> we now have a new code path which can trigger such case, change
> fixup_user_fault to look for VM_FAULT_HWPOISON.
>
> Also make hva_to_pfn_remapped check for -EHWPOISON and communicate the
> poison fault up to the user_mem_abort().

I would much prefer the KVM change be split out to its own patch, I see no
reason why it needs to be bundled with the fixup_user_fault() change. KVM will
set pfn to KVM_PFN_ERR_FAULT before and after the fixup_user_fault() change.

> Signed-off-by: Ankit Agrawal <[email protected]>
> ---
> mm/gup.c | 2 +-
> virt/kvm/kvm_main.c | 6 ++++++
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 231711efa390..b78af20a0f52 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1414,7 +1414,7 @@ int fixup_user_fault(struct mm_struct *mm,
> }
>
> if (ret & VM_FAULT_ERROR) {
> - int err = vm_fault_to_errno(ret, 0);
> + int err = vm_fault_to_errno(ret, FOLL_HWPOISON);
>
> if (err)
> return err;
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 486800a7024b..2ff067f21a7c 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2731,6 +2731,12 @@ kvm_pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool interruptible,
> r = hva_to_pfn_remapped(vma, addr, write_fault, writable, &pfn);
> if (r == -EAGAIN)
> goto retry;
> +
> + if (r == -EHWPOISON) {
> + pfn = KVM_PFN_ERR_HWPOISON;
> + goto exit;
> + }
> +
> if (r < 0)
> pfn = KVM_PFN_ERR_FAULT;

I vote for

if (r == -EHWPOISON)
pfn = KVM_PFN_ERR_HWPOISON;
else if (r < 0)
pfn = KVM_PFN_ERR_FAULT;

or even opportunstically fix the < 0 weirdness:

if (r == -EHWPOISON)
pfn = KVM_PFN_ERR_HWPOISON;
else if (r)
pfn = KVM_PFN_ERR_FAULT;

It's rather confusing to see a goto in one error path but an effective fallthrough
in a different error path, i.e. gives the impression that KVM_PFN_ERR_HWPOISON
has some special behavior that doesn't apply to KVM_PFN_ERR_FAULT.