[PATCH] arm32: fix flushcache syscall with device address

[Tian Tao]

An issue has been observed on our Kungpeng916 systems when using a PCI
express GPU. This occurs when a 32 bit application running on a 64 bit
kernel issues a cache flush operation to a memory address that is in
a PCI BAR of the GPU.The results in an illegal operation and
subsequent crash.

Signed-off-by: Tian Tao <tiantao6@xxxxxxxxxxxxx>
Signed-off-by: Lixin Chen <chenlixin1@xxxxxxxxxx>
Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxx>
---
 arch/arm64/kernel/sys_compat.c | 69 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/arch/arm64/kernel/sys_compat.c b/arch/arm64/kernel/sys_compat.c
index 3c18c24..6c07944 100644
--- a/arch/arm64/kernel/sys_compat.c
+++ b/arch/arm64/kernel/sys_compat.c
@@ -15,12 +15,74 @@
 #include <linux/slab.h>
 #include <linux/syscalls.h>
 #include <linux/uaccess.h>
+#include <linux/hugetlb.h>
 
 #include <asm/cacheflush.h>
 #include <asm/system_misc.h>
 #include <asm/tlbflush.h>
 #include <asm/unistd.h>
 
+static long __check_pt_cacheable(unsigned long vaddr)
+{
+	struct mm_struct *mm = current->mm;
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pudval_t pudval;
+	pmd_t *pmd;
+	pmdval_t pmdval;
+	pte_t *pte;
+	pteval_t pteval;
+	pgprot_t pgprot;
+
+	spin_lock(&mm->page_table_lock);
+	pgd = pgd_offset(mm, vaddr);
+	if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+		goto no_page;
+
+	p4d = p4d_offset(pgd, vaddr);
+	if (p4d_none(*p4d) || unlikely(p4d_bad(*p4d)))
+		goto no_page;
+
+	pud = pud_offset(p4d, vaddr);
+	if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+		goto no_page;
+	if (pud_huge(*pud)) {
+		pudval = pud_val(*pud);
+		pgprot = __pgprot(pudval);
+		goto out;
+	}
+
+	pmd = pmd_offset(pud, vaddr);
+	if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+		goto no_page;
+	if (pmd_huge(*pmd)) {
+		pmdval = pmd_val(*pmd);
+		pgprot = __pgprot(pmdval);
+		goto out;
+	}
+
+	pte = pte_offset_map(pmd, vaddr);
+	if (!pte_present(*pte) || pte_none(*pte))
+		goto no_page;
+	pteval = pte_val(*pte);
+	pgprot = __pgprot(pteval);
+
+out:
+	pgprot.pgprot &= PTE_ATTRINDX_MASK;
+	if (pgprot.pgprot != PTE_ATTRINDX(MT_NORMAL)) {
+		pr_debug("non-cache page pgprot value=0x%llx.\n",
+			pgprot.pgprot);
+		goto no_page;
+	}
+	spin_unlock(&mm->page_table_lock);
+	return 1;
+
+no_page:
+	spin_unlock(&mm->page_table_lock);
+	return 0;
+}
+
 static long
 __do_compat_cache_op(unsigned long start, unsigned long end)
 {
@@ -32,6 +94,13 @@ __do_compat_cache_op(unsigned long start, unsigned long end)
 		if (fatal_signal_pending(current))
 			return 0;
 
+		 /* do not flush page table is non-cacheable */
+		if (!__check_pt_cacheable(start)) {
+			cond_resched();
+			start += chunk;
+			continue;
+		}
+
 		if (cpus_have_const_cap(ARM64_WORKAROUND_1542419)) {
 			/*
 			 * The workaround requires an inner-shareable tlbi.
-- 
2.7.4