[patch V2 39/52] x86/fpu: Use pkru_write_default() in copy_init_fpstate_to_fpregs()

Thomas Gleixner
2021-06-14T16:40:01Z

There is no point in using copy_init_pkru_to_fpregs() which in turn calls
write_pkru(). write_pkru() tries to fiddle with the task's xstate buffer
for nothing because the XRSTOR[S](init_fpstate) just cleared the xfeature
flag in the xstate header which makes get_xsave_addr() fail.

It's a useless exercise anyway because the reinitialization activates the
FPU so before the task's xstate buffer can be used again a XRSTOR[S] must
happen which in turn dumps the PKRU value.

Get rid of the now unused copy_init_pkru_to_fpregs().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/include/asm/pkeys.h | 1 -
arch/x86/kernel/fpu/core.c | 3 +--
arch/x86/mm/pkeys.c | 17 -----------------
include/linux/pkeys.h | 4 ----
4 files changed, 1 insertion(+), 24 deletions(-)

--- a/arch/x86/include/asm/pkeys.h
+++ b/arch/x86/include/asm/pkeys.h
@@ -124,7 +124,6 @@ extern int arch_set_user_pkey_access(str
unsigned long init_val);
extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
unsigned long init_val);
-extern void copy_init_pkru_to_fpregs(void);

static inline int vma_pkey(struct vm_area_struct *vma)
{
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -377,8 +377,7 @@ static inline void load_fpregs_from_init
else
frstor_from_kernel(&init_fpstate.fsave);

- if (cpu_feature_enabled(X86_FEATURE_OSPKE))
- copy_init_pkru_to_fpregs();
+ pkru_write_default();
}

/*
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -10,7 +10,6 @@

#include <asm/cpufeature.h> /* boot_cpu_has, ... */
#include <asm/mmu_context.h> /* vma_pkey() */
-#include <asm/pkru.h> /* read/write_pkru() */

int __execute_only_pkey(struct mm_struct *mm)
{
@@ -125,22 +124,6 @@ u32 init_pkru_value = PKRU_AD_KEY( 1) |
PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) |
PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15);

-/*
- * Called from the FPU code when creating a fresh set of FPU
- * registers. This is called from a very specific context where
- * we know the FPU registers are safe for use and we can use PKRU
- * directly.
- */
-void copy_init_pkru_to_fpregs(void)
-{
- u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value);
- /*
- * Override the PKRU state that came from 'init_fpstate'
- * with the baseline from the process.
- */
- write_pkru(init_pkru_value_snapshot);
-}
-
static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
{
--- a/include/linux/pkeys.h
+++ b/include/linux/pkeys.h
@@ -44,10 +44,6 @@ static inline bool arch_pkeys_enabled(vo
return false;
}

-static inline void copy_init_pkru_to_fpregs(void)
-{
-}
-
#endif /* ! CONFIG_ARCH_HAS_PKEYS */

#endif /* _LINUX_PKEYS_H */