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Subject[PATCH v3] riscv: Ensure only ASIDLEN is used for sfence.vma
Date
From: Alistair Francis <alistair.francis@wdc.com>

When we set the value of context.id using __new_context() we set both
the asid and the current_version with this return statement in
__new_context():

return asid | ver;

This means that when local_flush_tlb_all_asid() is called with the asid
specified from context.id we can write the incorrect value.

We get away with this as hardware ignores the extra bits, as the RISC-V
specification states:

"bits SXLEN-1:ASIDMAX of the value held in rs2 are reserved for future
standard use. Until their use is defined by a standard extension, they
should be zeroed by software and ignored by current implementations."

but it is still a bug and worth addressing as we are incorrectly setting
extra bits.

This patch uses asid_mask when calling sfence.vma to ensure the asid is
always the correct len (ASIDLEN). This is similar to what we do in
arch/riscv/mm/context.c.

Fixes: 3f1e782998cd ("riscv: add ASID-based tlbflushing methods")
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
v3:
- Use helper function
v2:
- Pass in pre-masked value

arch/riscv/include/asm/mmu_context.h | 2 ++
arch/riscv/mm/context.c | 5 +++++
arch/riscv/mm/tlbflush.c | 2 +-
3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/mmu_context.h b/arch/riscv/include/asm/mmu_context.h
index 7030837adc1a..94e82c9e17eb 100644
--- a/arch/riscv/include/asm/mmu_context.h
+++ b/arch/riscv/include/asm/mmu_context.h
@@ -16,6 +16,8 @@
void switch_mm(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *task);

+unsigned long get_mm_asid(struct mm_struct *mm);
+
#define activate_mm activate_mm
static inline void activate_mm(struct mm_struct *prev,
struct mm_struct *next)
diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
index 7acbfbd14557..14aec5bacbc1 100644
--- a/arch/riscv/mm/context.c
+++ b/arch/riscv/mm/context.c
@@ -302,6 +302,11 @@ static inline void flush_icache_deferred(struct mm_struct *mm, unsigned int cpu)
#endif
}

+unsigned long get_mm_asid(struct mm_struct *mm)
+{
+ return atomic_long_read(&mm->context.id) & asid_mask;
+}
+
void switch_mm(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *task)
{
diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 37ed760d007c..9c89c4951bee 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -42,7 +42,7 @@ static void __sbi_tlb_flush_range(struct mm_struct *mm, unsigned long start,
/* check if the tlbflush needs to be sent to other CPUs */
broadcast = cpumask_any_but(cmask, cpuid) < nr_cpu_ids;
if (static_branch_unlikely(&use_asid_allocator)) {
- unsigned long asid = atomic_long_read(&mm->context.id);
+ unsigned long asid = get_mm_asid(mm);

if (broadcast) {
sbi_remote_sfence_vma_asid(cmask, start, size, asid);
--
2.35.1
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