Re: [PATCH 05/35] s390/mm: provide memory management functions for protected KVM guests

[David Hildenbrand <david@redhat.com>]

>  
>  /*
> @@ -1086,12 +1106,16 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
>  					    unsigned long addr,
>  					    pte_t *ptep, int full)
>  {
> +	pte_t res;

Empty line missing.

>  	if (full) {
> -		pte_t pte = *ptep;
> +		res = *ptep;
>  		*ptep = __pte(_PAGE_INVALID);
> -		return pte;
> +	} else {
> +		res = ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
>  	}
> -	return ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
> +	if (mm_is_protected(mm) && pte_present(res))
> +		uv_convert_from_secure(pte_val(res) & PAGE_MASK);
> +	return res;
>  }

[...]

> +int uv_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb);
> +int uv_convert_from_secure(unsigned long paddr);
> +
> +static inline int uv_convert_to_secure(struct gmap *gmap, unsigned long gaddr)
> +{
> +	struct uv_cb_cts uvcb = {
> +		.header.cmd = UVC_CMD_CONV_TO_SEC_STOR,
> +		.header.len = sizeof(uvcb),
> +		.guest_handle = gmap->guest_handle,
> +		.gaddr = gaddr,
> +	};
> +
> +	return uv_make_secure(gmap, gaddr, &uvcb);
> +}

I'd actually suggest to name everything that eats a gmap "gmap_",

e.g., "gmap_make_secure()"

[...]

>  
>  #if defined(CONFIG_PROTECTED_VIRTUALIZATION_GUEST) ||                          \
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index a06a628a88da..15ac598a3d8d 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -9,6 +9,8 @@
>  #include <linux/sizes.h>
>  #include <linux/bitmap.h>
>  #include <linux/memblock.h>
> +#include <linux/pagemap.h>
> +#include <linux/swap.h>
>  #include <asm/facility.h>
>  #include <asm/sections.h>
>  #include <asm/uv.h>
> @@ -99,4 +101,174 @@ void adjust_to_uv_max(unsigned long *vmax)
>  	if (prot_virt_host && *vmax > uv_info.max_sec_stor_addr)
>  		*vmax = uv_info.max_sec_stor_addr;
>  }
> +
> +static int __uv_pin_shared(unsigned long paddr)
> +{
> +	struct uv_cb_cfs uvcb = {
> +		.header.cmd	= UVC_CMD_PIN_PAGE_SHARED,
> +		.header.len	= sizeof(uvcb),
> +		.paddr		= paddr,

please drop all the superfluous spaces (just as in the other uv calls).

> +	};
> +
> +	if (uv_call(0, (u64)&uvcb))
> +		return -EINVAL;
> +	return 0;
> +}

[...]

> +static int make_secure_pte(pte_t *ptep, unsigned long addr, void *data)
> +{
> +	struct conv_params *params = data;
> +	pte_t entry = READ_ONCE(*ptep);
> +	struct page *page;
> +	int expected, rc = 0;
> +
> +	if (!pte_present(entry))
> +		return -ENXIO;
> +	if (pte_val(entry) & (_PAGE_INVALID | _PAGE_PROTECT))
> +		return -ENXIO;
> +
> +	page = pte_page(entry);
> +	if (page != params->page)
> +		return -ENXIO;
> +
> +	if (PageWriteback(page))
> +		return -EAGAIN;
> +	expected = expected_page_refs(page);

I do wonder if we could factor out expected_page_refs() and reuse from
other sources ...

I do wonder about huge page backing of guests, and especially
hpage_nr_pages(page) used in mm/migrate.c:expected_page_refs(). But I
can spot some hugepage exclusion below ... This needs comments.

> +	if (!page_ref_freeze(page, expected))
> +		return -EBUSY;
> +	set_bit(PG_arch_1, &page->flags);

Can we please document somewhere how PG_arch_1 is used on s390x? (page)

"The generic code guarantees that this bit is cleared for a page when it
first is entered into the page cache" - should not be an issue, right?

> +	rc = uv_call(0, (u64)params->uvcb);
> +	page_ref_unfreeze(page, expected);
> +	if (rc)
> +		rc = (params->uvcb->rc == 0x10a) ? -ENXIO : -EINVAL;
> +	return rc;
> +}
> +
> +/*
> + * Requests the Ultravisor to make a page accessible to a guest.
> + * If it's brought in the first time, it will be cleared. If
> + * it has been exported before, it will be decrypted and integrity
> + * checked.
> + *
> + * @gmap: Guest mapping
> + * @gaddr: Guest 2 absolute address to be imported

I'd just drop the the (incomplete) parameter documentation, everybody
reaching this point should now what a gmap and what a gaddr is ...

> + */
> +int uv_make_secure(struct gmap *gmap, unsigned long gaddr, void *uvcb)
> +{
> +	struct conv_params params = { .uvcb = uvcb };
> +	struct vm_area_struct *vma;
> +	unsigned long uaddr;
> +	int rc, local_drain = 0;
> +
> +again:
> +	rc = -EFAULT;
> +	down_read(&gmap->mm->mmap_sem);
> +
> +	uaddr = __gmap_translate(gmap, gaddr);
> +	if (IS_ERR_VALUE(uaddr))
> +		goto out;
> +	vma = find_vma(gmap->mm, uaddr);
> +	if (!vma)
> +		goto out;
> +	if (is_vm_hugetlb_page(vma))
> +		goto out;

Hah there it is! How is it enforced on upper layers/excluded? Will
hpage=true fail with prot virt? What if a guest is not a protected guest
but wants to sue huge pages? This needs comments/patch description.

> +
> +	rc = -ENXIO;
> +	params.page = follow_page(vma, uaddr, FOLL_WRITE | FOLL_NOWAIT);
> +	if (IS_ERR_OR_NULL(params.page))
> +		goto out;
> +
> +	lock_page(params.page);
> +	rc = apply_to_page_range(gmap->mm, uaddr, PAGE_SIZE, make_secure_pte, &params);

Ehm, isn't it just always a single page?

> +	unlock_page(params.page);
> +out:
> +	up_read(&gmap->mm->mmap_sem);
> +
> +	if (rc == -EBUSY) {
> +		if (local_drain) {
> +			lru_add_drain_all();
> +			return -EAGAIN;
> +		}
> +		lru_add_drain();

comments please why that is performed.

> +		local_drain = 1;
> +		goto again;

Could we end up in an endless loop?

> +	} else if (rc == -ENXIO) {
> +		if (gmap_fault(gmap, gaddr, FAULT_FLAG_WRITE))
> +			return -EFAULT;
> +		return -EAGAIN;
> +	}
> +	return rc;
> +}
> +EXPORT_SYMBOL_GPL(uv_make_secure);
> +
> +/**
> + * To be called with the page locked or with an extra reference!
> + */
> +int arch_make_page_accessible(struct page *page)
> +{
> +	int rc = 0;
> +
> +	if (PageHuge(page))
> +		return 0;

Ah, another instance. Comment please why

> +
> +	if (!test_bit(PG_arch_1, &page->flags))
> +		return 0;

"Can you describe the meaning of this bit with three words"? Or a couple
more? :D

"once upon a time, the page was secure and still might be" ?
"the page is secure and therefore inaccessible" ?

> +
> +	rc = __uv_pin_shared(page_to_phys(page));
> +	if (!rc) {
> +		clear_bit(PG_arch_1, &page->flags);
> +		return 0;
> +	}
> +
> +	rc = uv_convert_from_secure(page_to_phys(page));
> +	if (!rc) {
> +		clear_bit(PG_arch_1, &page->flags);
> +		return 0;
> +	}
> +
> +	return rc;
> +}
> +EXPORT_SYMBOL_GPL(arch_make_page_accessible);
> +
>  #endif
> 

More code comments would be highly appreciated!

-- 
Thanks,

David / dhildenb