[PATCH 4/4] powerpc/mm/radix: Workaround prefetch issue with KVM
Benjamin Herrenschmidt
benh at kernel.crashing.org
Fri Jul 14 16:25:59 AEST 2017
On Fri, 2017-07-14 at 11:21 +0530, Aneesh Kumar K.V wrote:
>
> > There is still an issue with malicious guests purposefully setting
> > the PID register to a value in the host range. Hopefully future HW
> > can prevent that, but in the meantime, we handle it with a pair of
> > kludges:
> >
> > - On the way out of a guest, before we clear the current VCPU
> > in the PACA, we check the PID and if it's outside of the permitted
> > range we flush the TLB for that PID.
>
> Can you explain more about this ? We still run with guest PIDR at this
> point right ? How does flushing TLB here prevent a further speculative
> access of Quadrant 0 ? Or is it that beyound this point such access is
> not possible ?
No, the code is buggy, it's supposed to be doing the test after we
restored the PIDR to the host PID but I somewhat fumbled that up.
I'll respin.
> >
> > - When context switching, if the mm is "new" on that CPU (the
> > corresponding bit was set for the first time in the mm cpumask), we
> > check if any sibling thread is in KVM (has a non-NULL VCPU pointer
> > in the PACA). If that is the case, we also flush the PID for that
> > CPU (core).
>
> This is needed so that we don't run with old stale translation details
> which was left in this core right ?
Sort of. What can happen is that before the above flushes the TLB, some
translations can come in, then be invalidated on the remote CPU but not
on this one*, then another thread of this core picks up the PID and
hits the now stale translations.
Very unlikely but theorically possible.
>
> >
> > This second part is needed to handle the case where a process is
> > migrated (or starts a new pthread) on a sibling thread of the CPU
> > coming out of KVM, as there's a window where stale translations
> > can exist before we detect it and flush them out.
> >
> > A future optimization could be added by keeping track of whether
> > the PID has ever been used and avoid doing that for completely
> > fresh PIDs. We could similarily mark PIDs that have been the subject of
> > a global invalidation as "fresh". But for now this will do.
> >
> > Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> > ---
> > ---
> > arch/powerpc/include/asm/book3s/64/mmu.h | 15 ++++----
> > .../powerpc/include/asm/book3s/64/tlbflush-radix.h | 3 ++
> > arch/powerpc/include/asm/mmu_context.h | 25 +++++++++----
> > arch/powerpc/kernel/head_32.S | 6 +--
> > arch/powerpc/kernel/swsusp.c | 2 +-
> > arch/powerpc/kvm/book3s_32_sr.S | 2 +-
> > arch/powerpc/kvm/book3s_hv_rmhandlers.S | 12 ++++++
> > arch/powerpc/mm/mmu_context_book3s64.c | 43 ++++++++++++++++++++--
> > arch/powerpc/mm/mmu_context_nohash.c | 4 +-
> > arch/powerpc/mm/pgtable-radix.c | 31 +++++++++++++++-
> > arch/powerpc/mm/pgtable_64.c | 3 ++
> > arch/powerpc/mm/tlb-radix.c | 10 +++--
> > drivers/cpufreq/pmac32-cpufreq.c | 2 +-
> > drivers/macintosh/via-pmu.c | 4 +-
> > 14 files changed, 131 insertions(+), 31 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
> > index 77529a3..5b4023c 100644
> > --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> > +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> > @@ -59,13 +59,14 @@ extern struct patb_entry *partition_tb;
> > #define PRTS_MASK 0x1f /* process table size field */
> > #define PRTB_MASK 0x0ffffffffffff000UL
> >
> > -/*
> > - * Limit process table to PAGE_SIZE table. This
> > - * also limit the max pid we can support.
> > - * MAX_USER_CONTEXT * 16 bytes of space.
> > - */
> > -#define PRTB_SIZE_SHIFT (CONTEXT_BITS + 4)
> > -#define PRTB_ENTRIES (1ul << CONTEXT_BITS)
> > +/* Number of supported PID bits */
> > +extern unsigned int mmu_pid_bits;
> > +
> > +/* Base PID to allocate from */
> > +extern unsigned int mmu_base_pid;
> > +
> > +#define PRTB_SIZE_SHIFT (mmu_pid_bits + 4)
> > +#define PRTB_ENTRIES (1ul << mmu_pid_bits)
> >
> > /*
> > * Power9 currently only support 64K partition table size.
> > diff --git a/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h b/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h
> > index 9b433a6..2e0a6b4 100644
> > --- a/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h
> > +++ b/arch/powerpc/include/asm/book3s/64/tlbflush-radix.h
> > @@ -21,10 +21,13 @@ extern void radix__flush_tlb_range(struct vm_area_struct *vma, unsigned long sta
> > extern void radix__flush_tlb_kernel_range(unsigned long start, unsigned long end);
> >
> > extern void radix__local_flush_tlb_mm(struct mm_struct *mm);
> > +extern void radix__local_flush_all_mm(struct mm_struct *mm);
> > extern void radix__local_flush_tlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
> > extern void radix__local_flush_tlb_page_psize(struct mm_struct *mm, unsigned long vmaddr,
> > int psize);
> > extern void radix__tlb_flush(struct mmu_gather *tlb);
> > +extern void radix_flush_pid(unsigned long pid);
> > +
> > #ifdef CONFIG_SMP
> > extern void radix__flush_tlb_mm(struct mm_struct *mm);
> > extern void radix__flush_tlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
> > diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
> > index da7e943..26a587a 100644
> > --- a/arch/powerpc/include/asm/mmu_context.h
> > +++ b/arch/powerpc/include/asm/mmu_context.h
> > @@ -45,13 +45,15 @@ extern void set_context(unsigned long id, pgd_t *pgd);
> >
> > #ifdef CONFIG_PPC_BOOK3S_64
> > extern void radix__switch_mmu_context(struct mm_struct *prev,
> > - struct mm_struct *next);
> > + struct mm_struct *next,
> > + bool new_on_cpu);
> > static inline void switch_mmu_context(struct mm_struct *prev,
> > struct mm_struct *next,
> > - struct task_struct *tsk)
> > + struct task_struct *tsk,
> > + bool new_on_cpu)
> > {
> > if (radix_enabled())
> > - return radix__switch_mmu_context(prev, next);
> > + return radix__switch_mmu_context(prev, next, new_on_cpu);
> > return switch_slb(tsk, next);
> > }
> >
> > @@ -60,8 +62,13 @@ extern void hash__reserve_context_id(int id);
> > extern void __destroy_context(int context_id);
> > static inline void mmu_context_init(void) { }
> > #else
> > -extern void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
> > - struct task_struct *tsk);
> > +extern void __switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
> > + struct task_struct *tsk);
> > +static inline void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
> > + struct task_struct *tsk, bool new_on_cpu)
> > +{
> > + __switch_mmu_context(prev, next, tsk);
> > +}
> > extern unsigned long __init_new_context(void);
> > extern void __destroy_context(unsigned long context_id);
> > extern void mmu_context_init(void);
> > @@ -79,9 +86,13 @@ static inline void switch_mm_irqs_off(struct mm_struct *prev,
> > struct mm_struct *next,
> > struct task_struct *tsk)
> > {
> > + bool new_on_cpu = false;
> > +
> > /* Mark this context has been used on the new CPU */
> > - if (!cpumask_test_cpu(smp_processor_id(), mm_cpumask(next)))
> > + if (!cpumask_test_cpu(smp_processor_id(), mm_cpumask(next))) {
> > cpumask_set_cpu(smp_processor_id(), mm_cpumask(next));
> > + new_on_cpu = true;
> > + }
> >
> > /* 32-bit keeps track of the current PGDIR in the thread struct */
> > #ifdef CONFIG_PPC32
> > @@ -113,7 +124,7 @@ static inline void switch_mm_irqs_off(struct mm_struct *prev,
> > * The actual HW switching method differs between the various
> > * sub architectures. Out of line for now
> > */
> > - switch_mmu_context(prev, next, tsk);
> > + switch_mmu_context(prev, next, tsk, new_on_cpu);
> > }
> >
> > static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> > diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
> > index e227342..a530124 100644
> > --- a/arch/powerpc/kernel/head_32.S
> > +++ b/arch/powerpc/kernel/head_32.S
> > @@ -1003,11 +1003,11 @@ start_here:
> > RFI
> >
> > /*
> > - * void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next);
> > + * void __switch_mmu_context(struct mm_struct *prev, struct mm_struct *next);
> > *
> > * Set up the segment registers for a new context.
> > */
> > -_ENTRY(switch_mmu_context)
> > +_ENTRY(__switch_mmu_context)
> > lwz r3,MMCONTEXTID(r4)
> > cmpwi cr0,r3,0
> > blt- 4f
> > @@ -1040,7 +1040,7 @@ _ENTRY(switch_mmu_context)
> > 4: trap
> > EMIT_BUG_ENTRY 4b,__FILE__,__LINE__,0
> > blr
> > -EXPORT_SYMBOL(switch_mmu_context)
> > +EXPORT_SYMBOL(__switch_mmu_context)
> >
> > /*
> > * An undocumented "feature" of 604e requires that the v bit
> > diff --git a/arch/powerpc/kernel/swsusp.c b/arch/powerpc/kernel/swsusp.c
> > index 0050b2d..9c32cfd 100644
> > --- a/arch/powerpc/kernel/swsusp.c
> > +++ b/arch/powerpc/kernel/swsusp.c
> > @@ -32,6 +32,6 @@ void save_processor_state(void)
> > void restore_processor_state(void)
> > {
> > #ifdef CONFIG_PPC32
> > - switch_mmu_context(current->active_mm, current->active_mm, NULL);
> > + __switch_mmu_context(current->active_mm, current->active_mm, NULL);
> > #endif
> > }
> > diff --git a/arch/powerpc/kvm/book3s_32_sr.S b/arch/powerpc/kvm/book3s_32_sr.S
> > index 7e06a6f..a1705d4 100644
> > --- a/arch/powerpc/kvm/book3s_32_sr.S
> > +++ b/arch/powerpc/kvm/book3s_32_sr.S
> > @@ -138,6 +138,6 @@
> > lwz r4, MM(r4)
> > tophys(r4, r4)
> > /* This only clobbers r0, r3, r4 and r5 */
> > - bl switch_mmu_context
> > + bl __switch_mmu_context
> >
> > .endm
> > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > index 6ea4b53..4fb3581b 100644
> > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
> > @@ -1522,6 +1522,18 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
> > std r6, VCPU_BESCR(r9)
> > stw r7, VCPU_GUEST_PID(r9)
> > std r8, VCPU_WORT(r9)
> > +
> > + /* Handle the case where the guest used an illegal PID */
> > + LOAD_REG_ADDR(r4, mmu_base_pid)
> > + lwz r3, 0(r4)
> > + cmpw cr0,r7,r3
> > + blt 1f
> > +
> > + /* Illegal PID, flush the TLB */
> > + bl radix_flush_pid
> > + ld r9, HSTATE_KVM_VCPU(r13)
> > +1:
> > +
> > BEGIN_FTR_SECTION
> > mfspr r5, SPRN_TCSCR
> > mfspr r6, SPRN_ACOP
> > diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
> > index abed1fe..183a67b 100644
> > --- a/arch/powerpc/mm/mmu_context_book3s64.c
> > +++ b/arch/powerpc/mm/mmu_context_book3s64.c
> > @@ -25,6 +25,10 @@
> > #include <asm/mmu_context.h>
> > #include <asm/pgalloc.h>
> >
> > +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> > +#include <asm/kvm_book3s_asm.h>
> > +#endif
> > +
> > #include "icswx.h"
> >
> > static DEFINE_SPINLOCK(mmu_context_lock);
> > @@ -126,9 +130,10 @@ static int hash__init_new_context(struct mm_struct *mm)
> > static int radix__init_new_context(struct mm_struct *mm)
> > {
> > unsigned long rts_field;
> > - int index;
> > + int index, max_id;
> >
> > - index = alloc_context_id(1, PRTB_ENTRIES - 1);
> > + max_id = (1 << mmu_pid_bits) - 1;
> > + index = alloc_context_id(mmu_base_pid, max_id);
> > if (index < 0)
> > return index;
> >
> > @@ -247,8 +252,40 @@ void destroy_context(struct mm_struct *mm)
> > }
> >
> > #ifdef CONFIG_PPC_RADIX_MMU
> > -void radix__switch_mmu_context(struct mm_struct *prev, struct mm_struct *next)
> > +void radix__switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
> > + bool new_on_cpu)
> > {
> > + /*
> > + * If this context hasn't run on that CPU before and KVM is
> > + * around, there's a slim chance that the guest on another
> > + * CPU just brought in obsolete translation into the TLB of
> > + * this CPU due to a bad prefetch using the guest PID on
> > + * the way into the hypervisor.
> > + *
> > + * We work around this here. If KVM is possible, we check if
> > + * any sibling thread is in KVM. If it is, the window may exist
> > + * and thus we flush that PID from the core.
> > + *
> > + * A potential future improvement would be to mark which PIDs
> > + * have never been used on the system and avoid it if the PID
> > + * is new and the process has no other cpumask bit set.
> > + */
> > +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> > + if (cpu_has_feature(CPU_FTR_HVMODE) && new_on_cpu) {
> > + int cpu = smp_processor_id();
> > + int sib = cpu_first_thread_sibling(cpu);
> > + bool flush = false;
> > +
> > + for (; sib <= cpu_last_thread_sibling(cpu) && !flush; sib++) {
> > + if (sib == cpu)
> > + continue;
> > + if (paca[sib].kvm_hstate.kvm_vcpu)
> > + flush = true;
> > + }
> > + if (flush)
> > + radix__local_flush_all_mm(next);
> > + }
> > +#endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
>
> Is it possible to avoid that #ifdef and add kvm helper for this ? That will also
> avoid that kvm header inclusion arc/powerpc/mm/*.c files.
>
>
> >
> > if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {
> > isync();
> > diff --git a/arch/powerpc/mm/mmu_context_nohash.c b/arch/powerpc/mm/mmu_context_nohash.c
> > index 4554d65..47d84d0 100644
> > --- a/arch/powerpc/mm/mmu_context_nohash.c
> > +++ b/arch/powerpc/mm/mmu_context_nohash.c
> > @@ -226,8 +226,8 @@ static void context_check_map(void)
> > static void context_check_map(void) { }
> > #endif
> >
> > -void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
> > - struct task_struct *tsk)
> > +void __switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
> > + struct task_struct *tsk)
> > {
> > unsigned int i, id, cpu = smp_processor_id();
> > unsigned long *map;
> > diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
> > index 83d70f7..3888aea 100644
> > --- a/arch/powerpc/mm/pgtable-radix.c
> > +++ b/arch/powerpc/mm/pgtable-radix.c
> > @@ -168,11 +168,34 @@ static void __init radix_init_pgtable(void)
> > for_each_memblock(memory, reg)
> > WARN_ON(create_physical_mapping(reg->base,
> > reg->base + reg->size));
> > +
> > + /* Find out how many PID bits are supported */
> > + if (cpu_has_feature(CPU_FTR_HVMODE)) {
> > + if (!mmu_pid_bits)
> > + mmu_pid_bits = 20;
> > +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
> > + /*
> > + * When KVM is possible, we only use the top half of the
> > + * PID space to avoid collisions between host and guest PIDs
> > + * which can cause problems due to prefetch when exiting the
> > + * guest with AIL=3
> > + */
> > + mmu_base_pid = 1 << (mmu_pid_bits - 1);
> > +#else
> > + mmu_base_pid = 1;
> > +#endif
> > + } else {
> > + /* The guest uses the bottom half of the PID space */
> > + if (!mmu_pid_bits)
> > + mmu_pid_bits = 19;
> > + mmu_base_pid = 1;
> > + }
> > +
> > /*
> > * Allocate Partition table and process table for the
> > * host.
> > */
> > - BUILD_BUG_ON_MSG((PRTB_SIZE_SHIFT > 36), "Process table size too large.");
> > + BUG_ON(PRTB_SIZE_SHIFT > 36);
> > process_tb = early_alloc_pgtable(1UL << PRTB_SIZE_SHIFT);
> > /*
> > * Fill in the process table.
> > @@ -245,6 +268,12 @@ static int __init radix_dt_scan_page_sizes(unsigned long node,
> > if (type == NULL || strcmp(type, "cpu") != 0)
> > return 0;
> >
> > + /* Find MMU PID size */
> > + prop = of_get_flat_dt_prop(node, "ibm,mmu-pid-bits", &size);
> > + if (prop && size == 4)
> > + mmu_pid_bits = be32_to_cpup(prop);
> > +
> > + /* Grab page size encodings */
> > prop = of_get_flat_dt_prop(node, "ibm,processor-radix-AP-encodings", &size);
> > if (!prop)
> > return 0;
> > diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
> > index b165bab..5cc73f1 100644
> > --- a/arch/powerpc/mm/pgtable_64.c
> > +++ b/arch/powerpc/mm/pgtable_64.c
> > @@ -68,6 +68,9 @@
> > */
> > struct prtb_entry *process_tb;
> > struct patb_entry *partition_tb;
> > +unsigned int mmu_pid_bits;
> > +unsigned int mmu_base_pid;
> > +
> > /*
> > * page table size
> > */
> > diff --git a/arch/powerpc/mm/tlb-radix.c b/arch/powerpc/mm/tlb-radix.c
> > index 73d3fbf..54d5c75 100644
> > --- a/arch/powerpc/mm/tlb-radix.c
> > +++ b/arch/powerpc/mm/tlb-radix.c
> > @@ -66,6 +66,12 @@ static inline void _tlbiel_pid(unsigned long pid, unsigned long ric)
> > asm volatile(PPC_INVALIDATE_ERAT "; isync" : : :"memory");
> > }
> >
> > +/* Used by KVM */
> > +void radix_flush_pid(unsigned long pid)
> > +{
> > + _tlbiel_pid(pid, RIC_FLUSH_ALL);
> > +}
> > +
> > static inline void _tlbie_pid(unsigned long pid, unsigned long ric)
> > {
> > unsigned long rb,rs,prs,r;
> > @@ -138,8 +144,7 @@ void radix__local_flush_tlb_mm(struct mm_struct *mm)
> > }
> > EXPORT_SYMBOL(radix__local_flush_tlb_mm);
> >
> > -#ifndef CONFIG_SMP
> > -static void radix__local_flush_all_mm(struct mm_struct *mm)
> > +void radix__local_flush_all_mm(struct mm_struct *mm)
> > {
> > unsigned long pid;
> >
> > @@ -149,7 +154,6 @@ static void radix__local_flush_all_mm(struct mm_struct *mm)
> > _tlbiel_pid(pid, RIC_FLUSH_ALL);
> > preempt_enable();
> > }
> > -#endif /* CONFIG_SMP */
> >
> > void radix__local_flush_tlb_page_psize(struct mm_struct *mm, unsigned long vmaddr,
> > int psize)
> > diff --git a/drivers/cpufreq/pmac32-cpufreq.c b/drivers/cpufreq/pmac32-cpufreq.c
> > index ff44016..51026f2 100644
> > --- a/drivers/cpufreq/pmac32-cpufreq.c
> > +++ b/drivers/cpufreq/pmac32-cpufreq.c
> > @@ -300,7 +300,7 @@ static int pmu_set_cpu_speed(int low_speed)
> > _set_L3CR(save_l3cr);
> >
> > /* Restore userland MMU context */
> > - switch_mmu_context(NULL, current->active_mm, NULL);
> > + __switch_mmu_context(NULL, current->active_mm, NULL);
> >
> > #ifdef DEBUG_FREQ
> > printk(KERN_DEBUG "HID1, after: %x\n", mfspr(SPRN_HID1));
> > diff --git a/drivers/macintosh/via-pmu.c b/drivers/macintosh/via-pmu.c
> > index cce99f7..c06f08d 100644
> > --- a/drivers/macintosh/via-pmu.c
> > +++ b/drivers/macintosh/via-pmu.c
> > @@ -1851,7 +1851,7 @@ static int powerbook_sleep_grackle(void)
> > _set_L2CR(save_l2cr);
> >
> > /* Restore userland MMU context */
> > - switch_mmu_context(NULL, current->active_mm, NULL);
> > + __switch_mmu_context(NULL, current->active_mm, NULL);
> >
> > /* Power things up */
> > pmu_unlock();
> > @@ -1940,7 +1940,7 @@ powerbook_sleep_Core99(void)
> > _set_L3CR(save_l3cr);
> >
> > /* Restore userland MMU context */
> > - switch_mmu_context(NULL, current->active_mm, NULL);
> > + __switch_mmu_context(NULL, current->active_mm, NULL);
> >
> > /* Tell PMU we are ready */
> > pmu_unlock();
> > --
> > 2.9.4
More information about the Linuxppc-dev
mailing list