| Message ID | 20241013132520.2848-1-jszhang@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ARM: NOMMU: Fix exc_ret for stack frame type | expand |
On 10/13/24 14:25, Jisheng Zhang wrote: > commit 72cd4064fcca ("ARM: 8830/1: NOMMU: Toggle only bits in > EXC_RETURN we are really care of") only sets BIT[3] for Thread mode > and BIT[2] for PSP, it leaves BIT[4] untouched. But there's such a > case: the pre-linux env makes use of FPU then the BIT[4] in 'lr' is > cleared, this brings an umatch issue since the NOMMU kernel doesn't Can pre-linux env disable FPU before passing control to kernel (which is, as correctly pointed, doesn't know how to use FPU)? Cheers Vladimir
On Mon, Oct 14, 2024 at 10:54:00AM +0100, Vladimir Murzin wrote: > On 10/13/24 14:25, Jisheng Zhang wrote: > > commit 72cd4064fcca ("ARM: 8830/1: NOMMU: Toggle only bits in > > EXC_RETURN we are really care of") only sets BIT[3] for Thread mode > > and BIT[2] for PSP, it leaves BIT[4] untouched. But there's such a > > case: the pre-linux env makes use of FPU then the BIT[4] in 'lr' is > > cleared, this brings an umatch issue since the NOMMU kernel doesn't > > Can pre-linux env disable FPU before passing control to kernel (which > is, as correctly pointed, doesn't know how to use FPU)? IIRC, I did a experiment like this by clearing the SCB CPACR related bits, but the stack frame type is still not correct. I searched in the armv8m arm or cortex-mN's TRM I didn't find the relation between the returned "lr" and the pre FPU usage. What's more, IMHO, kernel needs to use the correct exc_ret no matter the pre-linux env does, I.E if kernel/userspace supports FPU, then clear BIT[4]; if no, set BIT[4]. PS: this is a regression: before the commit, the have-used-fpu pre-linux env + linux nommu combination works; after the commit, it fails to execute the init due to wrong stack frame type. Thanks
On 10/15/24 01:02, Jisheng Zhang wrote: > On Mon, Oct 14, 2024 at 10:54:00AM +0100, Vladimir Murzin wrote: >> On 10/13/24 14:25, Jisheng Zhang wrote: >>> commit 72cd4064fcca ("ARM: 8830/1: NOMMU: Toggle only bits in >>> EXC_RETURN we are really care of") only sets BIT[3] for Thread mode >>> and BIT[2] for PSP, it leaves BIT[4] untouched. But there's such a >>> case: the pre-linux env makes use of FPU then the BIT[4] in 'lr' is >>> cleared, this brings an umatch issue since the NOMMU kernel doesn't >> Can pre-linux env disable FPU before passing control to kernel (which >> is, as correctly pointed, doesn't know how to use FPU)? > IIRC, I did a experiment like this by clearing the SCB CPACR related > bits, but the stack frame type is still not correct. I searched in the > armv8m arm or cortex-mN's TRM I didn't find the relation between the > returned "lr" and the pre FPU usage. > > What's more, IMHO, kernel needs to use the correct exc_ret no matter > the pre-linux env does, I.E if kernel/userspace supports FPU, then > clear BIT[4]; if no, set BIT[4]. > > PS: this is a regression: before the commit, the have-used-fpu pre-linux > env + linux nommu combination works; after the commit, it fails to > execute the init due to wrong stack frame type. > > Thanks > Fair enough. Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com> Please, upload the patch in RMK's patch system [1] [1] https://www.arm.linux.org.uk/developer/patches/ Vladimir
diff --git a/arch/arm/include/asm/v7m.h b/arch/arm/include/asm/v7m.h index 4512f7e1918f..3aea6d3c97ee 100644 --- a/arch/arm/include/asm/v7m.h +++ b/arch/arm/include/asm/v7m.h @@ -51,6 +51,7 @@ */ #define EXC_RET_STACK_MASK 0x00000004 #define EXC_RET_THREADMODE_PROCESSSTACK (3 << 2) +#define EXC_RET_FTYPE (1 << 4) /* Cache related definitions */ diff --git a/arch/arm/mm/proc-v7m.S b/arch/arm/mm/proc-v7m.S index ed7781c84341..fdae077d2654 100644 --- a/arch/arm/mm/proc-v7m.S +++ b/arch/arm/mm/proc-v7m.S @@ -138,6 +138,7 @@ __v7m_setup_cont: 1: cpsid i /* Calculate exc_ret */ orr r10, lr, #EXC_RET_THREADMODE_PROCESSSTACK + orr r10, #EXC_RET_FTYPE ldmia sp, {r0-r3, r12} str r5, [r12, #11 * 4] @ restore the original SVC vector entry mov lr, r6 @ restore LR
commit 72cd4064fcca ("ARM: 8830/1: NOMMU: Toggle only bits in EXC_RETURN we are really care of") only sets BIT[3] for Thread mode and BIT[2] for PSP, it leaves BIT[4] untouched. But there's such a case: the pre-linux env makes use of FPU then the BIT[4] in 'lr' is cleared, this brings an umatch issue since the NOMMU kernel doesn't support FPU yet. Before the above commit, we hardcode the exc_ret as 0xfffffffd, so the flow works fine. Fix this issue by explicitly set BIT[4] which means using standard stack frame. Fixes: 72cd4064fcca ("ARM: 8830/1: NOMMU: Toggle only bits in EXC_RETURN we are really care of") Signed-off-by: Jisheng Zhang <jszhang@kernel.org> --- arch/arm/include/asm/v7m.h | 1 + arch/arm/mm/proc-v7m.S | 1 + 2 files changed, 2 insertions(+)