[tip: x86/pasid] x86/mmu: Allocate/free a PASID

tip-bot2 for Fenghua Yu
2020-09-18T07:42:34Z

The following commit has been merged into the x86/pasid branch of tip:

Commit-ID: 20f0afd1fb3d7d44f4a3db5a4b6e904410862140
Gitweb: https://git.kernel.org/tip/20f0afd1fb3d7d44f4a3db5a4b6e904410862140
Author: Fenghua Yu <fenghua.yu@intel.com>
AuthorDate: Tue, 15 Sep 2020 09:30:13 -07:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Thu, 17 Sep 2020 20:22:15 +02:00

x86/mmu: Allocate/free a PASID

A PASID is allocated for an "mm" the first time any thread binds to an
SVA-capable device and is freed from the "mm" when the SVA is unbound
by the last thread. It's possible for the "mm" to have different PASID
values in different binding/unbinding SVA cycles.

The mm's PASID (non-zero for valid PASID or 0 for invalid PASID) is
propagated to a per-thread PASID MSR for all threads within the mm
through IPI, context switch, or inherited. This is done to ensure that a
running thread has the right PASID in the MSR matching the mm's PASID.

[ bp: s/SVM/SVA/g; massage. ]

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lkml.kernel.org/r/1600187413-163670-10-git-send-email-fenghua.yu@intel.com
---
arch/x86/include/asm/fpu/api.h | 12 ++++++-
arch/x86/include/asm/fpu/internal.h | 7 +++-
arch/x86/kernel/fpu/xstate.c | 57 ++++++++++++++++++++++++++++-
drivers/iommu/intel/svm.c | 28 +++++++++++++-
4 files changed, 103 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index b774c52..dcd9503 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -62,4 +62,16 @@ extern void switch_fpu_return(void);
*/
extern int cpu_has_xfeatures(u64 xfeatures_mask, const char **feature_name);

+/*
+ * Tasks that are not using SVA have mm->pasid set to zero to note that they
+ * will not have the valid bit set in MSR_IA32_PASID while they are running.
+ */
+#define PASID_DISABLED 0
+
+#ifdef CONFIG_IOMMU_SUPPORT
+/* Update current's PASID MSR/state by mm's PASID. */
+void update_pasid(void);
+#else
+static inline void update_pasid(void) { }
+#endif
#endif /* _ASM_X86_FPU_API_H */
diff --git a/arch/x86/include/asm/fpu/internal.h b/arch/x86/include/asm/fpu/internal.h
index 0a460f2..341d00e 100644
--- a/arch/x86/include/asm/fpu/internal.h
+++ b/arch/x86/include/asm/fpu/internal.h
@@ -583,6 +583,13 @@ static inline void switch_fpu_finish(struct fpu *new_fpu)
pkru_val = pk->pkru;
}
__write_pkru(pkru_val);
+
+ /*
+ * Expensive PASID MSR write will be avoided in update_pasid() because
+ * TIF_NEED_FPU_LOAD was set. And the PASID state won't be updated
+ * unless it's different from mm->pasid to reduce overhead.
+ */
+ update_pasid();
}

/*
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 67f1a03..5d80474 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -1402,3 +1402,60 @@ int proc_pid_arch_status(struct seq_file *m, struct pid_namespace *ns,
return 0;
}
#endif /* CONFIG_PROC_PID_ARCH_STATUS */
+
+#ifdef CONFIG_IOMMU_SUPPORT
+void update_pasid(void)
+{
+ u64 pasid_state;
+ u32 pasid;
+
+ if (!cpu_feature_enabled(X86_FEATURE_ENQCMD))
+ return;
+
+ if (!current->mm)
+ return;
+
+ pasid = READ_ONCE(current->mm->pasid);
+ /* Set the valid bit in the PASID MSR/state only for valid pasid. */
+ pasid_state = pasid == PASID_DISABLED ?
+ pasid : pasid | MSR_IA32_PASID_VALID;
+
+ /*
+ * No need to hold fregs_lock() since the task's fpstate won't
+ * be changed by others (e.g. ptrace) while the task is being
+ * switched to or is in IPI.
+ */
+ if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
+ /* The MSR is active and can be directly updated. */
+ wrmsrl(MSR_IA32_PASID, pasid_state);
+ } else {
+ struct fpu *fpu = &current->thread.fpu;
+ struct ia32_pasid_state *ppasid_state;
+ struct xregs_state *xsave;
+
+ /*
+ * The CPU's xstate registers are not currently active. Just
+ * update the PASID state in the memory buffer here. The
+ * PASID MSR will be loaded when returning to user mode.
+ */
+ xsave = &fpu->state.xsave;
+ xsave->header.xfeatures |= XFEATURE_MASK_PASID;
+ ppasid_state = get_xsave_addr(xsave, XFEATURE_PASID);
+ /*
+ * Since XFEATURE_MASK_PASID is set in xfeatures, ppasid_state
+ * won't be NULL and no need to check its value.
+ *
+ * Only update the task's PASID state when it's different
+ * from the mm's pasid.
+ */
+ if (ppasid_state->pasid != pasid_state) {
+ /*
+ * Invalid fpregs so that state restoring will pick up
+ * the PASID state.
+ */
+ __fpu_invalidate_fpregs_state(fpu);
+ ppasid_state->pasid = pasid_state;
+ }
+ }
+}
+#endif /* CONFIG_IOMMU_SUPPORT */
diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index fc90a07..60ffe08 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -19,6 +19,7 @@
#include <linux/mm_types.h>
#include <linux/ioasid.h>
#include <asm/page.h>
+#include <asm/fpu/api.h>

#include "pasid.h"

@@ -444,6 +445,24 @@ out:
return ret;
}

+static void _load_pasid(void *unused)
+{
+ update_pasid();
+}
+
+static void load_pasid(struct mm_struct *mm, u32 pasid)
+{
+ mutex_lock(&mm->context.lock);
+
+ /* Synchronize with READ_ONCE in update_pasid(). */
+ smp_store_release(&mm->pasid, pasid);
+
+ /* Update PASID MSR on all CPUs running the mm's tasks. */
+ on_each_cpu_mask(mm_cpumask(mm), _load_pasid, NULL, true);
+
+ mutex_unlock(&mm->context.lock);
+}
+
/* Caller must hold pasid_mutex, mm reference */
static int
intel_svm_bind_mm(struct device *dev, unsigned int flags,
@@ -591,6 +610,10 @@ intel_svm_bind_mm(struct device *dev, unsigned int flags,
}

list_add_tail(&svm->list, &global_svm_list);
+ if (mm) {
+ /* The newly allocated pasid is loaded to the mm. */
+ load_pasid(mm, svm->pasid);
+ }
} else {
/*
* Binding a new device with existing PASID, need to setup
@@ -654,8 +677,11 @@ static int intel_svm_unbind_mm(struct device *dev, u32 pasid)

if (list_empty(&svm->devs)) {
ioasid_free(svm->pasid);
- if (svm->mm)
+ if (svm->mm) {
mmu_notifier_unregister(&svm->notifier, svm->mm);
+ /* Clear mm's pasid. */
+ load_pasid(svm->mm, PASID_DISABLED);
+ }
list_del(&svm->list);
/* We mandate that no page faults may be outstanding
* for the PASID when intel_svm_unbind_mm() is called.