[PATCH v2 2/3] arm64: hwpoison: add VM_FAULT_HWPOISON[_LARGE] handling

Will Deacon [off-list ref] writes:

On Wed, May 17, 2017 at 04:23:35PM +0100, Punit Agrawal wrote:

quoted

From: "Jonathan (Zhixiong) Zhang" <redacted>

Add VM_FAULT_HWPOISON[_LARGE] handling to the arm64 page fault
handler. Handling of VM_FAULT_HWPOISON[_LARGE] is very similar
to VM_FAULT_OOM, the only difference is that a different si_code
(BUS_MCEERR_AR) is passed to user space and si_addr_lsb field is
initialized.

Signed-off-by: Jonathan (Zhixiong) Zhang <redacted>
Signed-off-by: Tyler Baicar <redacted>
(fix new __do_user_fault call-site)
Signed-off-by: Punit Agrawal <redacted>
Acked-by: Steve Capper <redacted>
---
 arch/arm64/mm/fault.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 37b95dff0b07..a85b44343ac6 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c

@@ -31,6 +31,7 @@
 #include <linux/highmem.h>
 #include <linux/perf_event.h>
 #include <linux/preempt.h>
+#include <linux/hugetlb.h>
 
 #include <asm/bug.h>
 #include <asm/cpufeature.h>

@@ -239,10 +240,11 @@ static void __do_kernel_fault(struct mm_struct *mm, unsigned long addr,
  */
 static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 			    unsigned int esr, unsigned int sig, int code,
-			    struct pt_regs *regs)
+			    struct pt_regs *regs, int fault)
 {
 	struct siginfo si;
 	const struct fault_info *inf;
+	unsigned int lsb = 0;
 
 	if (unhandled_signal(tsk, sig) && show_unhandled_signals_ratelimited()) {
 		inf = esr_to_fault_info(esr);

@@ -259,6 +261,17 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 	si.si_errno = 0;
 	si.si_code = code;
 	si.si_addr = (void __user *)addr;
+	/*
+	 * Either small page or large page may be poisoned.
+	 * In other words, VM_FAULT_HWPOISON_LARGE and
+	 * VM_FAULT_HWPOISON are mutually exclusive.
+	 */
+	if (fault & VM_FAULT_HWPOISON_LARGE)
+		lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
+	else if (fault & VM_FAULT_HWPOISON)
+		lsb = PAGE_SHIFT;
+	si.si_addr_lsb = lsb;
+

If we're going to start handling poison faults, then we should probably
rejig the perf page fault accounting around here so that we follow x86:

  * Always report PERF_COUNT_SW_PAGE_FAULTS,
  * Don't report anything else for VM_FAULT_ERROR
  * Report PERF_COUNT_SW_PAGE_FAULTS_MAJ if VM_FAULT_MAJOR
  * Otherwise, report PERF_COUNT_SW_PAGE_FAULTS_MIN

at the moment, I think you're accounting VM_FAULT_ERROR as
PERF_COUNT_SW_PAGE_FAULTS_MIN, which doesn't feel right at all.

Ok. I'd missed the implication of enabling poisoned pages fault handling
on the perf accounting. I'll add a patch to update the reporting.

Will