[PATCH] add icswx support
Tseng-Hui (Frank) Lin
thlin at linux.vnet.ibm.com
Wed Apr 28 07:56:50 EST 2010
On Sat, 2010-04-24 at 10:55 +1000, Benjamin Herrenschmidt wrote:
> On Fri, 2010-04-23 at 17:04 -0500, Tseng-Hui (Frank) Lin wrote:
> > Add Power7 icswx co-processor instruction support.
>
> Please provide a -much- more detailed explanation of what it is, what it
> does and why it requires hooking into the MMU context switch code. _I_
> know these things but nobody else on the list does which limits the
> ability of people to review your patch.
>
icswx is a PowerPC co-processor instruction to send data to a
co-processor. On Book-S processors the LPAR_ID and process ID (PID) of
the owning process are registered in the window context of the
co-processor at initial time. When the icswx instruction is executed,
the L2 generates a cop-reg transaction on PowerBus. The transaction has
no address and the processor does not perform an MMU access to
authenticate the transaction. The coprocessor compares the LPAR_ID and
the PID included in the transaction and the LPAR_ID and PID held in the
window context to determine if the process is authorized to generate the
transaction.
> > Signed-off-by: Sonny Rao <sonnyrao at linux.vnet.ibm.com>
> > Signed-off-by: Tseng-Hui (Frank) Lin <thlin at linux.vnet.ibm.com>
> > ---
> > arch/powerpc/include/asm/mmu-hash64.h | 3 +
> > arch/powerpc/include/asm/mmu_context.h | 4 ++
> > arch/powerpc/include/asm/reg.h | 3 +
> > arch/powerpc/mm/mmu_context_hash64.c | 79
> > ++++++++++++++++++++++++++++++++
> > 4 files changed, 89 insertions(+), 0 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/mmu-hash64.h
> > b/arch/powerpc/include/asm/mmu-hash64.h
> > index 2102b21..ba5727d 100644
> > --- a/arch/powerpc/include/asm/mmu-hash64.h
> > +++ b/arch/powerpc/include/asm/mmu-hash64.h
> > @@ -421,6 +421,9 @@ typedef struct {
> > #ifdef CONFIG_PPC_SUBPAGE_PROT
> > struct subpage_prot_table spt;
> > #endif /* CONFIG_PPC_SUBPAGE_PROT */
> > + unsigned long acop;
> > +#define HASH64_MAX_PID (0xFFFF)
> > + unsigned int pid;
>
> Please add a comment as to what those two fields are about, something
> like acop; /* mask of enabled coprocessor types */ and pid /* pid
> value used with coprocessors */ or something like that.
>
> > } mm_context_t;
> >
> >
> > diff --git a/arch/powerpc/include/asm/mmu_context.h
> > b/arch/powerpc/include/asm/mmu_context.h
> > index 26383e0..d6c8841 100644
> > --- a/arch/powerpc/include/asm/mmu_context.h
> > +++ b/arch/powerpc/include/asm/mmu_context.h
> > @@ -78,6 +78,10 @@ static inline void switch_mm(struct mm_struct *prev,
> > struct mm_struct *next,
> >
> > #define deactivate_mm(tsk,mm) do { } while (0)
> >
> > +extern void switch_cop(struct mm_struct *next);
> > +extern int use_cop(unsigned long acop, struct task_struct *task);
> ^ remove that space
> > +extern void disuse_cop(unsigned long acop, struct mm_struct *mm);
>
> I'd prefer "drop" or "forget" :-)
>
> > +
> > /*
> > * After we have set current->mm to a new value, this activates
> > * the context for the new mm so we see the new mappings.
> > diff --git a/arch/powerpc/include/asm/reg.h
> > b/arch/powerpc/include/asm/reg.h
> > index 5572e86..30503f8 100644
> > --- a/arch/powerpc/include/asm/reg.h
> > +++ b/arch/powerpc/include/asm/reg.h
> > @@ -516,6 +516,9 @@
> > #define SPRN_SIAR 780
> > #define SPRN_SDAR 781
> >
> > +#define SPRN_ACOP 31
> > +#define SPRN_PID 48
> > +
>
> Remove the definition of SPRN_PID from reg_booke.h to avoid a double
> definition then.
>
> > #define SPRN_PA6T_MMCR0 795
> > #define PA6T_MMCR0_EN0 0x0000000000000001UL
> > #define PA6T_MMCR0_EN1 0x0000000000000002UL
> > diff --git a/arch/powerpc/mm/mmu_context_hash64.c
> > b/arch/powerpc/mm/mmu_context_hash64.c
> > index 2535828..d0a79f6 100644
> > --- a/arch/powerpc/mm/mmu_context_hash64.c
> > +++ b/arch/powerpc/mm/mmu_context_hash64.c
> > @@ -18,6 +18,7 @@
> > #include <linux/mm.h>
> > #include <linux/spinlock.h>
> > #include <linux/idr.h>
> > +#include <linux/percpu.h>
> > #include <linux/module.h>
> > #include <linux/gfp.h>
> >
> > @@ -25,6 +26,82 @@
> >
> > static DEFINE_SPINLOCK(mmu_context_lock);
> > static DEFINE_IDA(mmu_context_ida);
> > +static DEFINE_IDA(cop_ida);
> > +
> > +/* Lazy switch the ACOP register */
> > +static DEFINE_PER_CPU(unsigned long, acop_reg);
> > +
> > +void switch_cop(struct mm_struct *next)
> > +{
> > + mtspr(SPRN_PID, next->context.pid);
> > + if (next->context.pid &&
> > + __get_cpu_var(acop_reg) != next->context.acop) {
> > + mtspr(SPRN_ACOP, next->context.acop);
> > + __get_cpu_var(acop_reg) = next->context.acop;
> > + }
> > +}
>
> The above doesn't appear to be called anywhere ?
>
> > +int use_cop(unsigned long acop, struct task_struct *task)
> > +{
> > + int pid;
> > + int err;
> > + struct mm_struct *mm = get_task_mm(task);
> > +
> > + if (!mm)
> > + return -EINVAL;
> > +
> > + if (!mm->context.pid) {
> > + if (!ida_pre_get(&cop_ida, GFP_KERNEL))
> > + return -ENOMEM;
> > +again:
> > + spin_lock(&mmu_context_lock);
> > + err = ida_get_new_above(&cop_ida, 1, &pid);
> > + spin_unlock(&mmu_context_lock);
> > +
> > + if (err == -EAGAIN)
> > + goto again;
> > + else if (err)
> > + return err;
> > +
> > + if (pid > HASH64_MAX_PID) {
> > + spin_lock(&mmu_context_lock);
> > + ida_remove(&cop_ida, pid);
> > + spin_unlock(&mmu_context_lock);
> > + return -EBUSY;
> > + }
> > + mm->context.pid = pid;
> > + mtspr(SPRN_PID, mm->context.pid);
>
> Shouldn't the above be ?
>
> if (mm == current->active_mm)
> mtspr(....)
>
> > + }
> > + mm->context.acop |= acop;
>
> Locking ?
>
> > + get_cpu_var(acop_reg) = mm->context.acop;
> > + mtspr(SPRN_ACOP, mm->context.acop);
>
> Same comment about testing for current.
>
> > + put_cpu_var(acop_reg);
> > +
> > + return mm->context.pid;
> > +}
> > +EXPORT_SYMBOL(use_cop);
> > +
> > +void disuse_cop(unsigned long acop, struct mm_struct *mm)
> > +{
> > + if (WARN_ON(!mm))
> > + return;
> > +
> > + mm->context.acop &= ~acop;
>
> Shouldn't the above need some kind of locking if multiple threads hit it
> with different "acop" values ?
>
> > + if (!mm->context.acop) {
> > + spin_lock(&mmu_context_lock);
> > + ida_remove(&cop_ida, mm->context.pid);
> > + spin_unlock(&mmu_context_lock);
> > + mm->context.pid = 0;
> > + mtspr(SPRN_PID, 0);
>
> Same comment about current.
>
> > + } else {
> > + get_cpu_var(acop_reg) = mm->context.acop;
> > + mtspr(SPRN_ACOP, mm->context.acop);
>
> Same comment.
>
> > + put_cpu_var(acop_reg);
> > + }
> > + mmput(mm);
> > +}
> > +EXPORT_SYMBOL(disuse_cop);
> >
> > /*
> > * The proto-VSID space has 2^35 - 1 segments available for user
> > mappings.
> > @@ -94,6 +171,8 @@ EXPORT_SYMBOL_GPL(__destroy_context);
> > void destroy_context(struct mm_struct *mm)
> > {
> > __destroy_context(mm->context.id);
> > + if (mm->context.pid)
> > + ida_remove(&cop_ida, mm->context.pid);
> > subpage_prot_free(mm);
> > mm->context.id = NO_CONTEXT;
> > }
>
> Cheers,
> Ben.
>
>
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