Re: [PATCH V4 8/8] riscv: Add config of thread stack size

Guo Ren
2022-09-21T08:25:20Z

On Wed, Sep 21, 2022 at 2:13 PM Guo Ren <guoren@kernel.org> wrote:
>
> On Tue, Sep 20, 2022 at 3:18 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Tue, Sep 20, 2022, at 2:46 AM, Guo Ren wrote:
> >
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index dfe600f3526c..8def456f328c 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -442,6 +442,16 @@ config IRQ_STACKS
> > > Add independent irq & softirq stacks for percpu to prevent
> > > kernel stack
> > > overflows. We may save some memory footprint by disabling IRQ_STACKS.
> > >
> > > +config THREAD_SIZE
> > > + int "Kernel stack size (in bytes)" if EXPERT
> > > + range 4096 65536
> > > + default 8192 if 32BIT && !KASAN
> > > + default 32768 if 64BIT && KASAN
> > > + default 16384
> > > + help
> > > + Specify the Pages of thread stack size (from 4KB to 64KB), which also
> > > + affects irq stack size, which is equal to thread stack size.
> >
> > I still think this should be guarded in a way that prevents
> > setting the stack to smaller than default values unless VMAP_STACK
> > is set as well.
> Current VMAP_STACK would double THREAD_SIZE. Let me see how to reduce
> the VMAP_STACK.
Sorry, for my miss understanding. I have no idea to reduce the
VMAP_STACK's THREAD_ALIGN, THREAD_SIZE*2 is fine. Here is my new
patch:

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 76bde12d9f8c..669ae57356a2 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -443,6 +443,16 @@ config IRQ_STACKS
Add independent irq & softirq stacks for percpu to prevent
kernel stack
overflows. We may save some memory footprint by disabling IRQ_STACKS.

+config THREAD_SIZE
+ int "Kernel stack size (in bytes)" if VMAP_STACK && EXPERT
+ range 4096 65536
+ default 8192 if 32BIT && !KASAN
+ default 32768 if 64BIT && KASAN
+ default 16384
+ help
+ Specify the Pages of thread stack size (from 4KB to 64KB), which also
+ affects irq stack size, which is equal to thread stack size.
+
endmenu # "Platform type"

menu "Kernel features"
diff --git a/arch/riscv/include/asm/thread_info.h
b/arch/riscv/include/asm/thread_info.h
index 043da8ccc7e6..e7ae3f13b879 100644
--- a/arch/riscv/include/asm/thread_info.h
+++ b/arch/riscv/include/asm/thread_info.h
@@ -11,32 +11,17 @@
#include <asm/page.h>
#include <linux/const.h>

-#ifdef CONFIG_KASAN
-#define KASAN_STACK_ORDER 1
-#else
-#define KASAN_STACK_ORDER 0
-#endif
-
/* thread information allocation */
-#ifdef CONFIG_64BIT
-#define THREAD_SIZE_ORDER (2 + KASAN_STACK_ORDER)
-#else
-#define THREAD_SIZE_ORDER (1 + KASAN_STACK_ORDER)
-#endif
-#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)
+#define THREAD_SIZE CONFIG_THREAD_SIZE

/*
* By aligning VMAP'd stacks to 2 * THREAD_SIZE, we can detect overflow by
- * checking sp & (1 << THREAD_SHIFT), which we can do cheaply in the entry
- * assembly.
+ * checking sp & THREAD_SIZE, which we can do cheaply in the entry assembly.
*/
#ifdef CONFIG_VMAP_STACK
#define THREAD_ALIGN (2 * THREAD_SIZE)
-#else
-#define THREAD_ALIGN THREAD_SIZE
#endif

-#define THREAD_SHIFT (PAGE_SHIFT + THREAD_SIZE_ORDER)
#define OVERFLOW_STACK_SIZE SZ_4K
#define SHADOW_OVERFLOW_STACK_SIZE (1024)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 2207cf44a3bc..71ea850ff0db 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -29,8 +29,8 @@ _restore_kernel_tpsp:

#ifdef CONFIG_VMAP_STACK
addi sp, sp, -(PT_SIZE_ON_STACK)
- srli sp, sp, THREAD_SHIFT
- andi sp, sp, 0x1
+ srli sp, sp, PAGE_SHIFT
+ andi sp, sp, (THREAD_ALIGN >> PAGE_SHIFT >> 1)
bnez sp, handle_kernel_stack_overflow
REG_L sp, TASK_TI_KERNEL_SP(tp)
#endif

>
> >
> > Arnd
>
>
>
> --
> Best Regards
> Guo Ren

--
Best Regards
Guo Ren