Re: [PATCH] x86, paravirt, xen: Remove the 64-bit irq_enable_sysexit pvop

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Apr 03, 2015 at 03:52:30PM -0700, Andy Lutomirski wrote:
> [cc: Boris and Konrad.  Whoops]
> 
> On Fri, Apr 3, 2015 at 3:51 PM, Andy Lutomirski <luto@kernel.org> wrote:
> > We don't use irq_enable_sysexit on 64-bit kernels any more.  Remove

Is there an commit (or name of patch) that explains why 32-bit-user-space-on-64-bit
kernels is unsavory?

Thank you!
> > all the paravirt and Xen machinery to support it on 64-bit kernels.
> >
> > Signed-off-by: Andy Lutomirski <luto@kernel.org>
> > ---
> >
> > I haven't actually tested this on Xen, but it builds for me.
> >
> >  arch/x86/ia32/ia32entry.S             |  6 ------
> >  arch/x86/include/asm/paravirt_types.h |  7 ++++---
> >  arch/x86/kernel/asm-offsets.c         |  2 ++
> >  arch/x86/kernel/paravirt.c            |  4 +++-
> >  arch/x86/kernel/paravirt_patch_64.c   |  1 -
> >  arch/x86/xen/enlighten.c              |  3 ++-
> >  arch/x86/xen/xen-asm_64.S             | 16 ----------------
> >  arch/x86/xen/xen-ops.h                |  2 ++
> >  8 files changed, 13 insertions(+), 28 deletions(-)
> >
> > diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> > index 5d8f987a340d..eb1eb7b70f4b 100644
> > --- a/arch/x86/ia32/ia32entry.S
> > +++ b/arch/x86/ia32/ia32entry.S
> > @@ -77,12 +77,6 @@ ENTRY(native_usergs_sysret32)
> >         swapgs
> >         sysretl
> >  ENDPROC(native_usergs_sysret32)
> > -
> > -ENTRY(native_irq_enable_sysexit)
> > -       swapgs
> > -       sti
> > -       sysexit
> > -ENDPROC(native_irq_enable_sysexit)
> >  #endif
> >
> >  /*
> > diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> > index 7549b8b369e4..38a0ff9ef06e 100644
> > --- a/arch/x86/include/asm/paravirt_types.h
> > +++ b/arch/x86/include/asm/paravirt_types.h
> > @@ -160,13 +160,14 @@ struct pv_cpu_ops {
> >         u64 (*read_pmc)(int counter);
> >         unsigned long long (*read_tscp)(unsigned int *aux);
> >
> > +#ifdef CONFIG_X86_32
> >         /*
> >          * Atomically enable interrupts and return to userspace.  This
> > -        * is only ever used to return to 32-bit processes; in a
> > -        * 64-bit kernel, it's used for 32-on-64 compat processes, but
> > -        * never native 64-bit processes.  (Jump, not call.)
> > +        * is only used in 32-bit kernels.  64-bit kernels use
> > +        * usergs_sysret32 instead.
> >          */
> >         void (*irq_enable_sysexit)(void);
> > +#endif
> >
> >         /*
> >          * Switch to usermode gs and return to 64-bit usermode using
> > diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
> > index 9f6b9341950f..2d27ebf0aed8 100644
> > --- a/arch/x86/kernel/asm-offsets.c
> > +++ b/arch/x86/kernel/asm-offsets.c
> > @@ -49,7 +49,9 @@ void common(void) {
> >         OFFSET(PV_IRQ_irq_disable, pv_irq_ops, irq_disable);
> >         OFFSET(PV_IRQ_irq_enable, pv_irq_ops, irq_enable);
> >         OFFSET(PV_CPU_iret, pv_cpu_ops, iret);
> > +#ifdef CONFIG_X86_32
> >         OFFSET(PV_CPU_irq_enable_sysexit, pv_cpu_ops, irq_enable_sysexit);
> > +#endif
> >         OFFSET(PV_CPU_read_cr0, pv_cpu_ops, read_cr0);
> >         OFFSET(PV_MMU_read_cr2, pv_mmu_ops, read_cr2);
> >  #endif
> > diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> > index 548d25f00c90..7563114d9c3a 100644
> > --- a/arch/x86/kernel/paravirt.c
> > +++ b/arch/x86/kernel/paravirt.c
> > @@ -154,7 +154,9 @@ unsigned paravirt_patch_default(u8 type, u16 clobbers, void *insnbuf,
> >                 ret = paravirt_patch_ident_64(insnbuf, len);
> >
> >         else if (type == PARAVIRT_PATCH(pv_cpu_ops.iret) ||
> > +#ifdef CONFIG_X86_32
> >                  type == PARAVIRT_PATCH(pv_cpu_ops.irq_enable_sysexit) ||
> > +#endif
> >                  type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret32) ||
> >                  type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret64))
> >                 /* If operation requires a jmp, then jmp */
> > @@ -371,7 +373,7 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
> >
> >         .load_sp0 = native_load_sp0,
> >
> > -#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
> > +#if defined(CONFIG_X86_32)
> >         .irq_enable_sysexit = native_irq_enable_sysexit,
> >  #endif
> >  #ifdef CONFIG_X86_64
> > diff --git a/arch/x86/kernel/paravirt_patch_64.c b/arch/x86/kernel/paravirt_patch_64.c
> > index a1da6737ba5b..0de21c62c348 100644
> > --- a/arch/x86/kernel/paravirt_patch_64.c
> > +++ b/arch/x86/kernel/paravirt_patch_64.c
> > @@ -49,7 +49,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
> >                 PATCH_SITE(pv_irq_ops, save_fl);
> >                 PATCH_SITE(pv_irq_ops, irq_enable);
> >                 PATCH_SITE(pv_irq_ops, irq_disable);
> > -               PATCH_SITE(pv_cpu_ops, irq_enable_sysexit);
> >                 PATCH_SITE(pv_cpu_ops, usergs_sysret32);
> >                 PATCH_SITE(pv_cpu_ops, usergs_sysret64);
> >                 PATCH_SITE(pv_cpu_ops, swapgs);
> > diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> > index 81665c9f2132..3797b6b31f95 100644
> > --- a/arch/x86/xen/enlighten.c
> > +++ b/arch/x86/xen/enlighten.c
> > @@ -1267,10 +1267,11 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst = {
> >         .read_tscp = native_read_tscp,
> >
> >         .iret = xen_iret,
> > -       .irq_enable_sysexit = xen_sysexit,
> >  #ifdef CONFIG_X86_64
> >         .usergs_sysret32 = xen_sysret32,
> >         .usergs_sysret64 = xen_sysret64,
> > +#else
> > +       .irq_enable_sysexit = xen_sysexit,
> >  #endif
> >
> >         .load_tr_desc = paravirt_nop,
> > diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
> > index 985fc3ee0973..a2cabb8bd6bf 100644
> > --- a/arch/x86/xen/xen-asm_64.S
> > +++ b/arch/x86/xen/xen-asm_64.S
> > @@ -47,22 +47,6 @@ ENTRY(xen_iret)
> >  ENDPATCH(xen_iret)
> >  RELOC(xen_iret, 1b+1)
> >
> > -/*
> > - * sysexit is not used for 64-bit processes, so it's only ever used to
> > - * return to 32-bit compat userspace.
> > - */
> > -ENTRY(xen_sysexit)
> > -       pushq $__USER32_DS
> > -       pushq %rcx
> > -       pushq $X86_EFLAGS_IF
> > -       pushq $__USER32_CS
> > -       pushq %rdx
> > -
> > -       pushq $0
> > -1:     jmp hypercall_iret
> > -ENDPATCH(xen_sysexit)
> > -RELOC(xen_sysexit, 1b+1)
> > -
> >  ENTRY(xen_sysret64)
> >         /*
> >          * We're already on the usermode stack at this point, but
> > diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
> > index 9e195c683549..c20fe29e65f4 100644
> > --- a/arch/x86/xen/xen-ops.h
> > +++ b/arch/x86/xen/xen-ops.h
> > @@ -134,7 +134,9 @@ DECL_ASM(void, xen_restore_fl_direct, unsigned long);
> >
> >  /* These are not functions, and cannot be called normally */
> >  __visible void xen_iret(void);
> > +#ifdef CONFIG_X86_32
> >  __visible void xen_sysexit(void);
> > +#endif
> >  __visible void xen_sysret32(void);
> >  __visible void xen_sysret64(void);
> >  __visible void xen_adjust_exception_frame(void);
> > --
> > 2.3.0
> >
> 
> 
> 
> -- 
> Andy Lutomirski
> AMA Capital Management, LLC