[PATCH V4 07/10] x86/pks: Preserve the PKRS MSR on context switch
From: ira . weiny
Date: Mon Mar 22 2021 - 01:31:53 EST
From: Ira Weiny <ira.weiny@xxxxxxxxx>
The PKRS MSR is defined as a per-logical-processor register. This
isolates memory access by logical CPU. Unfortunately, the MSR is not
managed by XSAVE. Therefore, tasks must save/restore the MSR value on
context switch.
Define a saved PKRS value in the task struct, as well as a cached
per-logical-processor MSR value which mirrors the MSR value of the
current CPU. Initialize all tasks with the default MSR value. Then, on
schedule in, call write_pkrs() which automatically avoids the overhead
of the MSR write if possible.
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Co-developed-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
---
Changes from V3
From Dan Williams
make pks_init_task() and pks_sched_in() macros
To avoid Supervisor PKey '#ifdefery' in process.c and
process_64.c
Use ARCH_ENABLE_SUPERVISOR_PKEYS
Split write_pkrs() to an earlier patch to be used in setup_pks()
Move Peter's authorship to that patch.
Remove kernel doc comment from write_pkrs
From Thomas Gleixner
Fix where pks_sched_in() is called from.
Should be called from __switch_to()
NOTE: PKS requires x86_64 so there is no need to
update process_32.c
Make pkrs_cache static
Remove unnecessary pkrs_cache declaration
Clean up formatting
Changes from V2
Adjust for PKS enable being final patch.
Changes from V1
Rebase to latest tip/master
Resolve conflicts with INIT_THREAD changes
Changes since RFC V3
Per Dave Hansen
Update commit message
move saved_pkrs to be in a nicer place
Per Peter Zijlstra
Add Comment from Peter
Clean up white space
Update authorship
---
arch/x86/include/asm/msr-index.h | 1 +
arch/x86/include/asm/pkeys_common.h | 14 ++++++++++
arch/x86/include/asm/processor.h | 43 ++++++++++++++++++++++++++++-
arch/x86/kernel/process.c | 3 ++
arch/x86/kernel/process_64.c | 2 ++
5 files changed, 62 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 546d6ecf0a35..c15a049bf6ac 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -765,6 +765,7 @@
#define MSR_IA32_TSC_DEADLINE 0x000006E0
+#define MSR_IA32_PKRS 0x000006E1
#define MSR_TSX_FORCE_ABORT 0x0000010F
diff --git a/arch/x86/include/asm/pkeys_common.h b/arch/x86/include/asm/pkeys_common.h
index 0681522974ba..6917f1a27479 100644
--- a/arch/x86/include/asm/pkeys_common.h
+++ b/arch/x86/include/asm/pkeys_common.h
@@ -17,4 +17,18 @@
#define PKR_AD_KEY(pkey) (PKR_AD_BIT << PKR_PKEY_SHIFT(pkey))
#define PKR_WD_KEY(pkey) (PKR_WD_BIT << PKR_PKEY_SHIFT(pkey))
+/*
+ * Define a default PKRS value for each task.
+ *
+ * Key 0 has no restriction. All other keys are set to the most restrictive
+ * value which is access disabled (AD=1).
+ *
+ * NOTE: This needs to be a macro to be used as part of the INIT_THREAD macro.
+ */
+#define INIT_PKRS_VALUE (PKR_AD_KEY(1) | PKR_AD_KEY(2) | PKR_AD_KEY(3) | \
+ PKR_AD_KEY(4) | PKR_AD_KEY(5) | PKR_AD_KEY(6) | \
+ PKR_AD_KEY(7) | PKR_AD_KEY(8) | PKR_AD_KEY(9) | \
+ PKR_AD_KEY(10) | PKR_AD_KEY(11) | PKR_AD_KEY(12) | \
+ PKR_AD_KEY(13) | PKR_AD_KEY(14) | PKR_AD_KEY(15))
+
#endif /*_ASM_X86_PKEYS_COMMON_H */
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index dc6d149bf851..b7ae396285dd 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -18,6 +18,7 @@ struct vm86;
#include <asm/cpufeatures.h>
#include <asm/page.h>
#include <asm/pgtable_types.h>
+#include <asm/pkeys_common.h>
#include <asm/percpu.h>
#include <asm/msr.h>
#include <asm/desc_defs.h>
@@ -519,6 +520,12 @@ struct thread_struct {
unsigned long cr2;
unsigned long trap_nr;
unsigned long error_code;
+
+#ifdef CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS
+ /* Saved Protection key register for supervisor mappings */
+ u32 saved_pkrs;
+#endif
+
#ifdef CONFIG_VM86
/* Virtual 86 mode info */
struct vm86 *vm86;
@@ -784,7 +791,41 @@ static inline void spin_lock_prefetch(const void *x)
#define KSTK_ESP(task) (task_pt_regs(task)->sp)
#else
-#define INIT_THREAD { }
+
+#ifdef CONFIG_ARCH_ENABLE_SUPERVISOR_PKEYS
+#define INIT_THREAD_PKRS .saved_pkrs = INIT_PKRS_VALUE
+
+void write_pkrs(u32 new_pkrs);
+
+/*
+ * Define pks_init_task and pks_sched_in as macros to avoid requiring the
+ * definition of struct task_struct in this header while keeping the supervisor
+ * pkey #ifdefery out of process.c and process_64.c
+ */
+
+/*
+ * New tasks get the most restrictive PKRS value.
+ */
+#define pks_init_task(tsk) \
+ tsk->thread.saved_pkrs = INIT_PKRS_VALUE;
+
+/*
+ * PKRS is only temporarily changed during specific code paths. Only a
+ * preemption during these windows away from the default value would
+ * require updating the MSR. write_pkrs() handles this optimization.
+ */
+#define pks_sched_in() \
+ write_pkrs(current->thread.saved_pkrs);
+
+#else
+#define INIT_THREAD_PKRS 0
+#define pks_init_task(tsk)
+#define pks_sched_in()
+#endif
+
+#define INIT_THREAD { \
+ INIT_THREAD_PKRS, \
+}
extern unsigned long KSTK_ESP(struct task_struct *task);
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 9c214d7085a4..89f8454a8541 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -43,6 +43,7 @@
#include <asm/io_bitmap.h>
#include <asm/proto.h>
#include <asm/frame.h>
+#include <asm/processor.h>
#include "process.h"
@@ -195,6 +196,8 @@ void flush_thread(void)
memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
fpu__clear_all(&tsk->thread.fpu);
+
+ pks_init_task(tsk);
}
void disable_TSC(void)
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index d08307df69ad..e590ecac1650 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -632,6 +632,8 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
/* Load the Intel cache allocation PQR MSR. */
resctrl_sched_in();
+ pks_sched_in();
+
return prev_p;
}
--
2.28.0.rc0.12.gb6a658bd00c9