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Message-ID: <dc0edfb4-d2bc-43be-9221-a1acb1cae5ec@kernel.org> Date: Tue, 16 Dec 2025 10:52:42 +0100 From: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org> To: Mukesh Kumar Chaurasiya <mkchauras@...ux.ibm.com>, maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com, oleg@...hat.com, kees@...nel.org, luto@...capital.net, wad@...omium.org, mchauras@...ux.ibm.com, thuth@...hat.com, sshegde@...ux.ibm.com, charlie@...osinc.com, macro@...am.me.uk, akpm@...ux-foundation.org, ldv@...ace.io, deller@....de, ankur.a.arora@...cle.com, segher@...nel.crashing.org, tglx@...utronix.de, thomas.weissschuh@...utronix.de, peterz@...radead.org, menglong8.dong@...il.com, bigeasy@...utronix.de, namcao@...utronix.de, kan.liang@...ux.intel.com, mingo@...nel.org, atrajeev@...ux.vnet.ibm.com, mark.barnett@....com, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 5/8] powerpc: add exit_flags field in pt_regs Le 14/12/2025 à 14:02, Mukesh Kumar Chaurasiya a écrit : > From: Mukesh Kumar Chaurasiya <mchauras@...ux.ibm.com> > > Add a new field `exit_flags` in the pt_regs structure. This field will hold > the flags set during interrupt or syscall execution that are required during > exit to user mode. > > Specifically, the `TIF_RESTOREALL` flag, stored in this field, helps the > exit routine determine if any NVGPRs were modified and need to be restored > before returning to userspace. In the current implementation we did our best to keep this information in a local var for performance reasons. Have you assessed the performance impact of going through the stack for that ? > > This addition ensures a clean and architecture-specific mechanism to track > per-syscall or per-interrupt state transitions related to register restore. > > Changes: > - Add `exit_flags` and `__pt_regs_pad` to maintain 16-byte stack alignment > - Update asm-offsets.c and ptrace.c for offset and validation > - Update PT_* constants in uapi header to reflect the new layout > > Signed-off-by: Mukesh Kumar Chaurasiya <mchauras@...ux.ibm.com> > --- > arch/powerpc/include/asm/ptrace.h | 3 +++ > arch/powerpc/include/uapi/asm/ptrace.h | 14 +++++++++----- > arch/powerpc/kernel/asm-offsets.c | 1 + > arch/powerpc/kernel/ptrace/ptrace.c | 1 + > 4 files changed, 14 insertions(+), 5 deletions(-) > > diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h > index 94aa1de2b06e..3af8a5898fe3 100644 > --- a/arch/powerpc/include/asm/ptrace.h > +++ b/arch/powerpc/include/asm/ptrace.h > @@ -53,6 +53,9 @@ struct pt_regs > unsigned long esr; > }; > unsigned long result; > + unsigned long exit_flags; > + /* Maintain 16 byte interrupt stack alignment */ On powerpc/32, one 'long' is 4 bytes not 8. > + unsigned long __pt_regs_pad[1]; > }; > }; > #if defined(CONFIG_PPC64) || defined(CONFIG_PPC_KUAP) > diff --git a/arch/powerpc/include/uapi/asm/ptrace.h b/arch/powerpc/include/uapi/asm/ptrace.h > index 01e630149d48..de56b216c9c5 100644 > --- a/arch/powerpc/include/uapi/asm/ptrace.h > +++ b/arch/powerpc/include/uapi/asm/ptrace.h > @@ -55,6 +55,8 @@ struct pt_regs > unsigned long dar; /* Fault registers */ > unsigned long dsisr; /* on 4xx/Book-E used for ESR */ > unsigned long result; /* Result of a system call */ > + unsigned long exit_flags; /* System call exit flags */ > + unsigned long __pt_regs_pad[1]; /* Maintain 16 byte interrupt stack alignment */ On powerpc/32, one 'long' is 4 bytes not 8. > }; > > #endif /* __ASSEMBLER__ */ > @@ -114,10 +116,12 @@ struct pt_regs > #define PT_DAR 41 > #define PT_DSISR 42 > #define PT_RESULT 43 > -#define PT_DSCR 44 > -#define PT_REGS_COUNT 44 > +#define PT_EXIT_FLAGS 44 > +#define PT_PAD 45 > +#define PT_DSCR 46 > +#define PT_REGS_COUNT 46 > > -#define PT_FPR0 48 /* each FP reg occupies 2 slots in this space */ > +#define PT_FPR0 (PT_REGS_COUNT + 4) /* each FP reg occupies 2 slots in this space */ > > #ifndef __powerpc64__ > > @@ -129,7 +133,7 @@ struct pt_regs > #define PT_FPSCR (PT_FPR0 + 32) /* each FP reg occupies 1 slot in 64-bit space */ > > > -#define PT_VR0 82 /* each Vector reg occupies 2 slots in 64-bit */ > +#define PT_VR0 (PT_FPSCR + 2) /* <82> each Vector reg occupies 2 slots in 64-bit */ > #define PT_VSCR (PT_VR0 + 32*2 + 1) > #define PT_VRSAVE (PT_VR0 + 33*2) > > @@ -137,7 +141,7 @@ struct pt_regs > /* > * Only store first 32 VSRs here. The second 32 VSRs in VR0-31 > */ > -#define PT_VSR0 150 /* each VSR reg occupies 2 slots in 64-bit */ > +#define PT_VSR0 (PT_VRSAVE + 2) /* each VSR reg occupies 2 slots in 64-bit */ > #define PT_VSR31 (PT_VSR0 + 2*31) > #endif /* __powerpc64__ */ > > diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c > index a4bc80b30410..c0bb09f1db78 100644 > --- a/arch/powerpc/kernel/asm-offsets.c > +++ b/arch/powerpc/kernel/asm-offsets.c > @@ -292,6 +292,7 @@ int main(void) > STACK_PT_REGS_OFFSET(_ESR, esr); > STACK_PT_REGS_OFFSET(ORIG_GPR3, orig_gpr3); > STACK_PT_REGS_OFFSET(RESULT, result); > + STACK_PT_REGS_OFFSET(EXIT_FLAGS, exit_flags); Where is that used ? > STACK_PT_REGS_OFFSET(_TRAP, trap); > #ifdef CONFIG_PPC64 > STACK_PT_REGS_OFFSET(SOFTE, softe); > diff --git a/arch/powerpc/kernel/ptrace/ptrace.c b/arch/powerpc/kernel/ptrace/ptrace.c > index c6997df63287..2134b6d155ff 100644 > --- a/arch/powerpc/kernel/ptrace/ptrace.c > +++ b/arch/powerpc/kernel/ptrace/ptrace.c > @@ -432,6 +432,7 @@ void __init pt_regs_check(void) > CHECK_REG(PT_DAR, dar); > CHECK_REG(PT_DSISR, dsisr); > CHECK_REG(PT_RESULT, result); > + CHECK_REG(PT_EXIT_FLAGS, exit_flags); > #undef CHECK_REG > > BUILD_BUG_ON(PT_REGS_COUNT != sizeof(struct user_pt_regs) / sizeof(unsigned long));
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