sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu

[PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller

Posted by Oleg Nesterov 9 months, 1 week ago

If CONFIG_X86_DEBUG_FPU=Y, arch_exit_to_user_mode_prepare() calls
arch_exit_work() even if ti_work == 0. There only reason is that we
want to call fpregs_assert_state_consistent() if TIF_NEED_FPU_LOAD
is not set.

This looks confusing. arch_exit_to_user_mode_prepare() can just call
fpregs_assert_state_consistent() unconditionally, it depends on
CONFIG_X86_DEBUG_FPU and checks TIF_NEED_FPU_LOAD itself.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 arch/x86/include/asm/entry-common.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 77d20555e04d..d535a97c7284 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -53,7 +53,6 @@ static inline void arch_exit_work(unsigned long ti_work)
 	if (unlikely(ti_work & _TIF_IO_BITMAP))
 		tss_update_io_bitmap();
 
-	fpregs_assert_state_consistent();
 	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
 }
@@ -61,7 +60,9 @@ static inline void arch_exit_work(unsigned long ti_work)
 static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 						  unsigned long ti_work)
 {
-	if (IS_ENABLED(CONFIG_X86_DEBUG_FPU) || unlikely(ti_work))
+	fpregs_assert_state_consistent();
+
+	if (unlikely(ti_work))
 		arch_exit_work(ti_work);
 
 	fred_update_rsp0();
-- 
2.25.1.362.g51ebf55

Re: [PATCH tip/x86/fpu 6/6] x86/fpu: shift fpregs_assert_state_consistent() from arch_exit_work() to its caller

Posted by Ingo Molnar 9 months, 1 week ago

* Oleg Nesterov <oleg@redhat.com> wrote:

> If CONFIG_X86_DEBUG_FPU=Y, arch_exit_to_user_mode_prepare() calls
> arch_exit_work() even if ti_work == 0. There only reason is that we
> want to call fpregs_assert_state_consistent() if TIF_NEED_FPU_LOAD
> is not set.
> 
> This looks confusing. arch_exit_to_user_mode_prepare() can just call
> fpregs_assert_state_consistent() unconditionally, it depends on
> CONFIG_X86_DEBUG_FPU and checks TIF_NEED_FPU_LOAD itself.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  arch/x86/include/asm/entry-common.h | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Thanks Oleg! I've applied these improvements to tip:x86/fpu.

Note that there's still a 32-bit hardened-usercopy regression/crash 
that Boris reported against tip:x86/fpu:

  https://lore.kernel.org/r/20250503120712.GJaBYG8A-D77MllFZ3@fat_crate.local

Which may result in the subsequent rebasing of your commits - but 
otherwise your series looks good to me.

Thanks,

	Ingo

[tip: x86/fpu] x86/fpu: Shift fpregs_assert_state_consistent() from arch_exit_work() to its caller

Posted by tip-bot2 for Oleg Nesterov 9 months, 1 week ago

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

Commit-ID:     46c158e3ad0fc633007802c338c409c188ec0a12
Gitweb:        https://git.kernel.org/tip/46c158e3ad0fc633007802c338c409c188ec0a12
Author:        Oleg Nesterov <oleg@redhat.com>
AuthorDate:    Sat, 03 May 2025 16:39:02 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Sun, 04 May 2025 10:29:25 +02:00

x86/fpu: Shift fpregs_assert_state_consistent() from arch_exit_work() to its caller

If CONFIG_X86_DEBUG_FPU=Y, arch_exit_to_user_mode_prepare() calls
arch_exit_work() even if ti_work == 0. There only reason is that we
want to call fpregs_assert_state_consistent() if TIF_NEED_FPU_LOAD
is not set.

This looks confusing. arch_exit_to_user_mode_prepare() can just call
fpregs_assert_state_consistent() unconditionally, it depends on
CONFIG_X86_DEBUG_FPU and checks TIF_NEED_FPU_LOAD itself.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Chang S . Bae <chang.seok.bae@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250503143902.GA9012@redhat.com
---
 arch/x86/include/asm/entry-common.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/entry-common.h b/arch/x86/include/asm/entry-common.h
index 77d2055..d535a97 100644
--- a/arch/x86/include/asm/entry-common.h
+++ b/arch/x86/include/asm/entry-common.h
@@ -53,7 +53,6 @@ static inline void arch_exit_work(unsigned long ti_work)
 	if (unlikely(ti_work & _TIF_IO_BITMAP))
 		tss_update_io_bitmap();
 
-	fpregs_assert_state_consistent();
 	if (unlikely(ti_work & _TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
 }
@@ -61,7 +60,9 @@ static inline void arch_exit_work(unsigned long ti_work)
 static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
 						  unsigned long ti_work)
 {
-	if (IS_ENABLED(CONFIG_X86_DEBUG_FPU) || unlikely(ti_work))
+	fpregs_assert_state_consistent();
+
+	if (unlikely(ti_work))
 		arch_exit_work(ti_work);
 
 	fred_update_rsp0();