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KVM: s390: A bugfix and a performance improvement

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* Improve interrupt cpu for wakeup, change the heuristic to decide wich
   vCPU to deliver a floating interrupt to.
 * Clear the pte when discarding a swapped page because of CMMA; this
   bug was introduced in 6.16 when refactoring gmap code.
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Merge tag 'kvm-s390-next-6.18-1' of https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD

KVM: s390: A bugfix and a performance improvement

* Improve interrupt cpu for wakeup, change the heuristic to decide wich
  vCPU to deliver a floating interrupt to.
* Clear the pte when discarding a swapped page because of CMMA; this
  bug was introduced in 6.16 when refactoring gmap code.
This commit is contained in:
Paolo Bonzini 2025-09-30 13:09:20 -04:00
commit 68f6051098
5 changed files with 44 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/s390/include/asm/kvm_host.h
View File

@ -356,7 +356,7 @@ struct kvm_s390_float_interrupt {
int counters[FIRQ_MAX_COUNT];
struct kvm_s390_mchk_info mchk;
struct kvm_s390_ext_info srv_signal;
int next_rr_cpu;
int last_sleep_cpu;
struct mutex ais_lock;
u8 simm;
u8 nimm;

22
arch/s390/include/asm/pgtable.h
View File

@ -2055,4 +2055,26 @@ static inline unsigned long gmap_pgste_get_pgt_addr(unsigned long *pgt)
return res;
}
static inline pgste_t pgste_get_lock(pte_t *ptep)
{
unsigned long value = 0;
#ifdef CONFIG_PGSTE
unsigned long *ptr = (unsigned long *)(ptep + PTRS_PER_PTE);
do {
value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);
} while (value & PGSTE_PCL_BIT);
value |= PGSTE_PCL_BIT;
#endif
return __pgste(value);
}
static inline void pgste_set_unlock(pte_t *ptep, pgste_t pgste)
{
#ifdef CONFIG_PGSTE
barrier();
WRITE_ONCE(*(unsigned long *)(ptep + PTRS_PER_PTE), pgste_val(pgste) & ~PGSTE_PCL_BIT);
#endif
}
#endif /* _S390_PAGE_H */

20
arch/s390/kvm/interrupt.c
View File

@ -1323,6 +1323,7 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu)
VCPU_EVENT(vcpu, 4, "enabled wait: %llu ns", sltime);
no_timer:
kvm_vcpu_srcu_read_unlock(vcpu);
vcpu->kvm->arch.float_int.last_sleep_cpu = vcpu->vcpu_idx;
kvm_vcpu_halt(vcpu);
vcpu->valid_wakeup = false;
__unset_cpu_idle(vcpu);
@ -1949,18 +1950,15 @@ static void __floating_irq_kick(struct kvm *kvm, u64 type)
if (!online_vcpus)
return;
/* find idle VCPUs first, then round robin */
sigcpu = find_first_bit(kvm->arch.idle_mask, online_vcpus);
if (sigcpu == online_vcpus) {
do {
sigcpu = kvm->arch.float_int.next_rr_cpu++;
kvm->arch.float_int.next_rr_cpu %= online_vcpus;
/* avoid endless loops if all vcpus are stopped */
if (nr_tries++ >= online_vcpus)
return;
} while (is_vcpu_stopped(kvm_get_vcpu(kvm, sigcpu)));
for (sigcpu = kvm->arch.float_int.last_sleep_cpu; ; sigcpu++) {
sigcpu %= online_vcpus;
dst_vcpu = kvm_get_vcpu(kvm, sigcpu);
if (!is_vcpu_stopped(dst_vcpu))
break;
/* avoid endless loops if all vcpus are stopped */
if (nr_tries++ >= online_vcpus)
return;
}
dst_vcpu = kvm_get_vcpu(kvm, sigcpu);
/* make the VCPU drop out of the SIE, or wake it up if sleeping */
switch (type) {

12
arch/s390/mm/gmap_helpers.c
View File

@ -15,6 +15,7 @@
#include <linux/pagewalk.h>
#include <linux/ksm.h>
#include <asm/gmap_helpers.h>
#include <asm/pgtable.h>
/**
* ptep_zap_swap_entry() - discard a swap entry.
@ -47,6 +48,7 @@ void gmap_helper_zap_one_page(struct mm_struct *mm, unsigned long vmaddr)
{
struct vm_area_struct *vma;
spinlock_t *ptl;
pgste_t pgste;
pte_t *ptep;
mmap_assert_locked(mm);
@ -60,8 +62,16 @@ void gmap_helper_zap_one_page(struct mm_struct *mm, unsigned long vmaddr)
ptep = get_locked_pte(mm, vmaddr, &ptl);
if (unlikely(!ptep))
return;
if (pte_swap(*ptep))
if (pte_swap(*ptep)) {
preempt_disable();
pgste = pgste_get_lock(ptep);
ptep_zap_swap_entry(mm, pte_to_swp_entry(*ptep));
pte_clear(mm, vmaddr, ptep);
pgste_set_unlock(ptep, pgste);
preempt_enable();
}
pte_unmap_unlock(ptep, ptl);
}
EXPORT_SYMBOL_GPL(gmap_helper_zap_one_page);

23
arch/s390/mm/pgtable.c
View File

@ -24,6 +24,7 @@
#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/page-states.h>
#include <asm/pgtable.h>
#include <asm/machine.h>
pgprot_t pgprot_writecombine(pgprot_t prot)
@ -115,28 +116,6 @@ static inline pte_t ptep_flush_lazy(struct mm_struct *mm,
return old;
}
static inline pgste_t pgste_get_lock(pte_t *ptep)
{
unsigned long value = 0;
#ifdef CONFIG_PGSTE
unsigned long *ptr = (unsigned long *)(ptep + PTRS_PER_PTE);
do {
value = __atomic64_or_barrier(PGSTE_PCL_BIT, ptr);
} while (value & PGSTE_PCL_BIT);
value |= PGSTE_PCL_BIT;
#endif
return __pgste(value);
}
static inline void pgste_set_unlock(pte_t *ptep, pgste_t pgste)
{
#ifdef CONFIG_PGSTE
barrier();
WRITE_ONCE(*(unsigned long *)(ptep + PTRS_PER_PTE), pgste_val(pgste) & ~PGSTE_PCL_BIT);
#endif
}
static inline pgste_t pgste_get(pte_t *ptep)
{
unsigned long pgste = 0;