[PATCHv3 4/8] x86/mm: Handle LAM on context switch

Kirill A. Shutemov
2022-06-10T14:35:42Z

Linear Address Masking mode for userspace pointers encoded in CR3 bits.
The mode is selected per-thread. Add new thread features indicate that the
thread has Linear Address Masking enabled.

switch_mm_irqs_off() now respects these flags and constructs CR3
accordingly.

The active LAM mode gets recorded in the tlb_state.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/include/asm/mmu.h | 1 +
arch/x86/include/asm/mmu_context.h | 24 ++++++++++++
arch/x86/include/asm/tlbflush.h | 3 ++
arch/x86/mm/tlb.c | 62 ++++++++++++++++++++++--------
4 files changed, 75 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index 5d7494631ea9..d150e92163b6 100644
--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -40,6 +40,7 @@ typedef struct {

#ifdef CONFIG_X86_64
unsigned short flags;
+ u64 lam_cr3_mask;
#endif

struct mutex lock;
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index b8d40ddeab00..e6eac047c728 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -91,6 +91,29 @@ static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
}
#endif

+#ifdef CONFIG_X86_64
+static inline u64 mm_cr3_lam_mask(struct mm_struct *mm)
+{
+ return mm->context.lam_cr3_mask;
+}
+
+static inline void dup_lam(struct mm_struct *oldmm, struct mm_struct *mm)
+{
+ mm->context.lam_cr3_mask = oldmm->context.lam_cr3_mask;
+}
+
+#else
+
+static inline u64 mm_cr3_lam_mask(struct mm_struct *mm)
+{
+ return 0;
+}
+
+static inline void dup_lam(struct mm_struct *oldmm, struct mm_struct *mm)
+{
+}
+#endif
+
#define enter_lazy_tlb enter_lazy_tlb
extern void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);

@@ -168,6 +191,7 @@ static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
{
arch_dup_pkeys(oldmm, mm);
paravirt_arch_dup_mmap(oldmm, mm);
+ dup_lam(oldmm, mm);
return ldt_dup_context(oldmm, mm);
}

diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
index 4af5579c7ef7..5b93dad93ff4 100644
--- a/arch/x86/include/asm/tlbflush.h
+++ b/arch/x86/include/asm/tlbflush.h
@@ -86,6 +86,9 @@ struct tlb_state {
unsigned long last_user_mm_spec;
};

+#ifdef CONFIG_X86_64
+ u64 lam_cr3_mask;
+#endif
u16 loaded_mm_asid;
u16 next_asid;

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index d400b6d9d246..458867a8f4bd 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -154,17 +154,17 @@ static inline u16 user_pcid(u16 asid)
return ret;
}

-static inline unsigned long build_cr3(pgd_t *pgd, u16 asid)
+static inline unsigned long build_cr3(pgd_t *pgd, u16 asid, u64 lam)
{
if (static_cpu_has(X86_FEATURE_PCID)) {
- return __sme_pa(pgd) | kern_pcid(asid);
+ return __sme_pa(pgd) | kern_pcid(asid) | lam;
} else {
VM_WARN_ON_ONCE(asid != 0);
- return __sme_pa(pgd);
+ return __sme_pa(pgd) | lam;
}
}

-static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
+static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid, u64 lam)
{
VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
/*
@@ -173,7 +173,7 @@ static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
* boot because all CPU's the have same capabilities:
*/
VM_WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_PCID));
- return __sme_pa(pgd) | kern_pcid(asid) | CR3_NOFLUSH;
+ return __sme_pa(pgd) | kern_pcid(asid) | lam | CR3_NOFLUSH;
}

/*
@@ -274,15 +274,15 @@ static inline void invalidate_user_asid(u16 asid)
(unsigned long *)this_cpu_ptr(&cpu_tlbstate.user_pcid_flush_mask));
}

-static void load_new_mm_cr3(pgd_t *pgdir, u16 new_asid, bool need_flush)
+static void load_new_mm_cr3(pgd_t *pgdir, u16 new_asid, u64 lam, bool need_flush)
{
unsigned long new_mm_cr3;

if (need_flush) {
invalidate_user_asid(new_asid);
- new_mm_cr3 = build_cr3(pgdir, new_asid);
+ new_mm_cr3 = build_cr3(pgdir, new_asid, lam);
} else {
- new_mm_cr3 = build_cr3_noflush(pgdir, new_asid);
+ new_mm_cr3 = build_cr3_noflush(pgdir, new_asid, lam);
}

/*
@@ -486,11 +486,36 @@ void cr4_update_pce(void *ignored)
static inline void cr4_update_pce_mm(struct mm_struct *mm) { }
#endif

+#ifdef CONFIG_X86_64
+static inline u64 tlbstate_lam_cr3_mask(void)
+{
+ return this_cpu_read(cpu_tlbstate.lam_cr3_mask);
+}
+
+static inline void set_tlbstate_lam_cr3_mask(u64 mask)
+{
+ this_cpu_write(cpu_tlbstate.lam_cr3_mask, mask);
+}
+
+#else
+
+static inline u64 tlbstate_lam_cr3_mask(void)
+{
+ return 0;
+}
+
+static inline void set_tlbstate_lam_cr3_mask(u64 mask)
+{
+}
+#endif
+
void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
struct task_struct *tsk)
{
struct mm_struct *real_prev = this_cpu_read(cpu_tlbstate.loaded_mm);
u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
+ u64 prev_lam = tlbstate_lam_cr3_mask();
+ u64 new_lam = mm_cr3_lam_mask(next);
bool was_lazy = this_cpu_read(cpu_tlbstate_shared.is_lazy);
unsigned cpu = smp_processor_id();
u64 next_tlb_gen;
@@ -504,6 +529,9 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
* cpu_tlbstate.loaded_mm) matches next.
*
* NB: leave_mm() calls us with prev == NULL and tsk == NULL.
+ *
+ * NB: Initial LAM enabling calls us with prev == next. We must update
+ * CR3 if prev_lam doesn't match the new one.
*/

/* We don't want flush_tlb_func() to run concurrently with us. */
@@ -520,7 +548,7 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
* isn't free.
*/
#ifdef CONFIG_DEBUG_VM
- if (WARN_ON_ONCE(__read_cr3() != build_cr3(real_prev->pgd, prev_asid))) {
+ if (WARN_ON_ONCE(__read_cr3() != build_cr3(real_prev->pgd, prev_asid, prev_lam))) {
/*
* If we were to BUG here, we'd be very likely to kill
* the system so hard that we don't see the call trace.
@@ -551,7 +579,7 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
* provides that full memory barrier and core serializing
* instruction.
*/
- if (real_prev == next) {
+ if (real_prev == next && prev_lam == new_lam) {
VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
next->context.ctx_id);

@@ -622,15 +650,16 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
barrier();
}

+ set_tlbstate_lam_cr3_mask(new_lam);
if (need_flush) {
this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id);
this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen);
- load_new_mm_cr3(next->pgd, new_asid, true);
+ load_new_mm_cr3(next->pgd, new_asid, new_lam, true);

trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
} else {
/* The new ASID is already up to date. */
- load_new_mm_cr3(next->pgd, new_asid, false);
+ load_new_mm_cr3(next->pgd, new_asid, new_lam, false);

trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, 0);
}
@@ -687,6 +716,7 @@ void initialize_tlbstate_and_flush(void)
struct mm_struct *mm = this_cpu_read(cpu_tlbstate.loaded_mm);
u64 tlb_gen = atomic64_read(&init_mm.context.tlb_gen);
unsigned long cr3 = __read_cr3();
+ u64 lam = cr3 & (X86_CR3_LAM_U48 | X86_CR3_LAM_U57);

/* Assert that CR3 already references the right mm. */
WARN_ON((cr3 & CR3_ADDR_MASK) != __pa(mm->pgd));
@@ -700,7 +730,7 @@ void initialize_tlbstate_and_flush(void)
!(cr4_read_shadow() & X86_CR4_PCIDE));

/* Force ASID 0 and force a TLB flush. */
- write_cr3(build_cr3(mm->pgd, 0));
+ write_cr3(build_cr3(mm->pgd, 0, lam));

/* Reinitialize tlbstate. */
this_cpu_write(cpu_tlbstate.last_user_mm_spec, LAST_USER_MM_INIT);
@@ -1047,8 +1077,10 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end)
*/
unsigned long __get_current_cr3_fast(void)
{
- unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
- this_cpu_read(cpu_tlbstate.loaded_mm_asid));
+ unsigned long cr3 =
+ build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
+ this_cpu_read(cpu_tlbstate.loaded_mm_asid),
+ tlbstate_lam_cr3_mask());

/* For now, be very restrictive about when this can be called. */
VM_WARN_ON(in_nmi() || preemptible());
--
2.35.1