Re: [PATCH v7 04/17] KVM: s390: pv: refactor s390_reset_acc

[Claudio Imbrenda]

On Mon, 7 Feb 2022 11:02:28 +0100
Janosch Frank <frankja@xxxxxxxxxxxxx> wrote:

> On 2/4/22 16:53, Claudio Imbrenda wrote:
> > Refactor s390_reset_acc so that it can be reused in upcoming patches.
> > 
> > We don't want to hold all the locks used in a walk_page_range for too
> > long, and the destroy page UVC does take some time to complete.
> > Therefore we quickly gather the pages to destroy, and then destroy them
> > without holding all the locks.
> > 
> > The new refactored function optionally allows to return early without
> > completing if a fatal signal is pending (and return and appropriate
> > error code). Two wrappers are provided to call the new function.
> > 
> > Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> > (dropping Janosch's Ack because of major changes to the patch)
> > ---
> >   arch/s390/include/asm/gmap.h | 36 +++++++++++++-
> >   arch/s390/kvm/pv.c           | 12 ++++-
> >   arch/s390/mm/gmap.c          | 95 +++++++++++++++++++++++++-----------
> >   3 files changed, 111 insertions(+), 32 deletions(-)
> > 
> > diff --git a/arch/s390/include/asm/gmap.h b/arch/s390/include/asm/gmap.h
> > index 746e18bf8984..2a913014f63c 100644
> > --- a/arch/s390/include/asm/gmap.h
> > +++ b/arch/s390/include/asm/gmap.h
> > @@ -147,7 +147,41 @@ int gmap_mprotect_notify(struct gmap *, unsigned long start,
> >   void gmap_sync_dirty_log_pmd(struct gmap *gmap, unsigned long dirty_bitmap[4],
> >   			     unsigned long gaddr, unsigned long vmaddr);
> >   int gmap_mark_unmergeable(void);
> > -void s390_reset_acc(struct mm_struct *mm);
> >   void s390_remove_old_asce(struct gmap *gmap);
> >   int s390_replace_asce(struct gmap *gmap);
> > +void s390_uv_destroy_pfns(unsigned long count, unsigned long *pfns);
> > +int __s390_uv_destroy_range(struct mm_struct *mm, unsigned long start,
> > +			    unsigned long end, int interruptible);  
> 
> s/int/bool/ ?

I don't know, I like the fact that the function could return
different error codes in the future if needed.

> 
> > +
> > +/**
> > + * s390_uv_destroy_range - Destroy a range of pages in the given mm.
> > + * @mm the mm on which to operate on
> > + * @start the start of the range
> > + * @end the end of the range
> > + *
> > + * This call will call cond_sched, so it should not generate stalls, but it  
> 
> This function will call ?

will fix

> 
> > + * will otherwise only return when it completed.
> > + */
> > +static inline void s390_uv_destroy_range(struct mm_struct *mm, unsigned long start,
> > +					 unsigned long end)
> > +{
> > +	(void)__s390_uv_destroy_range(mm, start, end, 0);
> > +}
> > +
> > +/**
> > + * s390_uv_destroy_range_interruptibe - Destroy a range of pages in the  
> 
> interruptible

will fix

> 
> > + * given mm, but stop when a fatal signal is received.
> > + * @mm the mm on which to operate on
> > + * @start the start of the range
> > + * @end the end of the range
> > + *
> > + * This call will call cond_sched, so it should not generate stalls.  It
> > + * will return -EINTR if a fatal signal is received, or 0 if the whole range
> > + * has been destroyed.
> > + */
> > +static inline int s390_uv_destroy_range_interruptible(struct mm_struct *mm, unsigned long start,
> > +						      unsigned long end)
> > +{
> > +	return __s390_uv_destroy_range(mm, start, end, 1);
> > +}
> >   #endif /* _ASM_S390_GMAP_H */
> > diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> > index 3c59ef763dde..2ab22500e092 100644
> > --- a/arch/s390/kvm/pv.c
> > +++ b/arch/s390/kvm/pv.c
> > @@ -12,6 +12,8 @@
> >   #include <asm/gmap.h>
> >   #include <asm/uv.h>
> >   #include <asm/mman.h>
> > +#include <linux/pagewalk.h>
> > +#include <linux/sched/mm.h>
> >   #include "kvm-s390.h"
> >   
> >   int kvm_s390_pv_destroy_cpu(struct kvm_vcpu *vcpu, u16 *rc, u16 *rrc)
> > @@ -157,8 +159,14 @@ int kvm_s390_pv_deinit_vm(struct kvm *kvm, u16 *rc, u16 *rrc)
> >   {
> >   	int cc;
> >   
> > -	/* make all pages accessible before destroying the guest */
> > -	s390_reset_acc(kvm->mm);
> > +	/*
> > +	 * if the mm still has a mapping, make all its pages accessible
> > +	 * before destroying the guest
> > +	 */
> > +	if (mmget_not_zero(kvm->mm)) {
> > +		s390_uv_destroy_range(kvm->mm, 0, TASK_SIZE);
> > +		mmput(kvm->mm);
> > +	}
> >   
> >   	cc = uv_cmd_nodata(kvm_s390_pv_get_handle(kvm),
> >   			   UVC_CMD_DESTROY_SEC_CONF, rc, rrc);
> > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> > index ce6cac4463f2..6eb5acb4be3d 100644
> > --- a/arch/s390/mm/gmap.c
> > +++ b/arch/s390/mm/gmap.c
> > @@ -2676,44 +2676,81 @@ void s390_reset_cmma(struct mm_struct *mm)
> >   }
> >   EXPORT_SYMBOL_GPL(s390_reset_cmma);
> >   
> > -/*
> > - * make inaccessible pages accessible again
> > - */
> > -static int __s390_reset_acc(pte_t *ptep, unsigned long addr,
> > -			    unsigned long next, struct mm_walk *walk)
> > +#define DESTROY_LOOP_THRESHOLD 32
> > +
> > +struct reset_walk_state {
> > +	unsigned long next;
> > +	unsigned long count;
> > +	unsigned long pfns[DESTROY_LOOP_THRESHOLD];
> > +};
> > +
> > +static int s390_gather_pages(pte_t *ptep, unsigned long addr,
> > +			     unsigned long next, struct mm_walk *walk)
> >   {
> > +	struct reset_walk_state *p = walk->private;
> >   	pte_t pte = READ_ONCE(*ptep);
> >   
> > -	/* There is a reference through the mapping */
> > -	if (pte_present(pte))
> > -		WARN_ON_ONCE(uv_destroy_owned_page(pte_val(pte) & PAGE_MASK));
> > -
> > -	return 0;
> > +	if (pte_present(pte)) {
> > +		/* we have a reference from the mapping, take an extra one */
> > +		get_page(phys_to_page(pte_val(pte)));
> > +		p->pfns[p->count] = phys_to_pfn(pte_val(pte));
> > +		p->next = next;
> > +		p->count++;
> > +	}
> > +	return p->count >= DESTROY_LOOP_THRESHOLD;
> >   }
> >   
> > -static const struct mm_walk_ops reset_acc_walk_ops = {
> > -	.pte_entry		= __s390_reset_acc,
> > +static const struct mm_walk_ops gather_pages_ops = {
> > +	.pte_entry = s390_gather_pages,
> >   };
> >   
> > -#include <linux/sched/mm.h>
> > -void s390_reset_acc(struct mm_struct *mm)
> > +/*
> > + * Call the Destroy secure page UVC on each page in the given array of PFNs.
> > + * Each page needs to have an extra reference, which will be released here.
> > + */
> > +void s390_uv_destroy_pfns(unsigned long count, unsigned long *pfns)
> >   {
> > -	if (!mm_is_protected(mm))
> > -		return;
> > -	/*
> > -	 * we might be called during
> > -	 * reset:                             we walk the pages and clear
> > -	 * close of all kvm file descriptors: we walk the pages and clear
> > -	 * exit of process on fd closure:     vma already gone, do nothing
> > -	 */
> > -	if (!mmget_not_zero(mm))
> > -		return;
> > -	mmap_read_lock(mm);
> > -	walk_page_range(mm, 0, TASK_SIZE, &reset_acc_walk_ops, NULL);
> > -	mmap_read_unlock(mm);
> > -	mmput(mm);
> > +	unsigned long i;
> > +
> > +	for (i = 0; i < count; i++) {
> > +		/* we always have an extra reference */
> > +		uv_destroy_owned_page(pfn_to_phys(pfns[i]));
> > +		/* get rid of the extra reference */
> > +		put_page(pfn_to_page(pfns[i]));
> > +		cond_resched();
> > +	}
> > +}
> > +EXPORT_SYMBOL_GPL(s390_uv_destroy_pfns);
> > +
> > +/**
> > + * __s390_uv_destroy_range - Walk the given range of the given address
> > + * space, and call the destroy secure page UVC on each page.
> > + * Optionally exit early if a fatal signal is pending.
> > + * @mm the mm to operate on
> > + * @start the start of the range
> > + * @end the end of the range
> > + * @interruptible if not 0, stop when a fatal signal is received
> > + * Return: 0 on success, -EINTR if the function stopped before completing
> > + */
> > +int __s390_uv_destroy_range(struct mm_struct *mm, unsigned long start,
> > +			    unsigned long end, int interruptible)
> > +{
> > +	struct reset_walk_state state = { .next = start };
> > +	int r = 1;
> > +
> > +	while (r > 0) {
> > +		state.count = 0;
> > +		mmap_read_lock(mm);
> > +		r = walk_page_range(mm, state.next, end, &gather_pages_ops, &state);
> > +		mmap_read_unlock(mm);
> > +		cond_resched();
> > +		s390_uv_destroy_pfns(state.count, state.pfns);
> > +		if (interruptible && fatal_signal_pending(current))
> > +			return -EINTR;
> > +	}
> > +	return 0;
> >   }
> > -EXPORT_SYMBOL_GPL(s390_reset_acc);
> > +EXPORT_SYMBOL_GPL(__s390_uv_destroy_range);
> >   
> >   /**
> >    * s390_remove_old_asce - Remove the topmost level of page tables from the
> >   
>