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Message-ID: <alpine.DEB.2.02.1507161707300.17378@kaball.uk.xensource.com>
Date: Thu, 16 Jul 2015 18:12:54 +0100
From: Stefano Stabellini <stefano.stabellini@...citrix.com>
To: Julien Grall <julien.grall@...rix.com>
CC: <xen-devel@...ts.xenproject.org>,
<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
"David Vrabel" <david.vrabel@...rix.com>
Subject: Re: [PATCH v2 19/20] xen/privcmd: Add support for Linux 64KB page
granularity
On Thu, 9 Jul 2015, Julien Grall wrote:
> The hypercall interface (as well as the toolstack) is always using 4KB
> page granularity. When the toolstack is asking for mapping a series of
> guest PFN in a batch, it expects to have the page map contiguously in
> its virtual memory.
>
> When Linux is using 64KB page granularity, the privcmd driver will have
> to map multiple Xen PFN in a single Linux page.
>
> Note that this solution works on page granularity which is a multiple of
> 4KB.
>
> Signed-off-by: Julien Grall <julien.grall@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> ---
> Changes in v2:
> - Use xen_apply_to_page
> ---
> drivers/xen/privcmd.c | 8 +--
> drivers/xen/xlate_mmu.c | 127 +++++++++++++++++++++++++++++++++---------------
> 2 files changed, 92 insertions(+), 43 deletions(-)
>
> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> index 5a29616..e8714b4 100644
> --- a/drivers/xen/privcmd.c
> +++ b/drivers/xen/privcmd.c
> @@ -446,7 +446,7 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
> return -EINVAL;
> }
>
> - nr_pages = m.num;
> + nr_pages = DIV_ROUND_UP_ULL(m.num, PAGE_SIZE / XEN_PAGE_SIZE);
> if ((m.num <= 0) || (nr_pages > (LONG_MAX >> PAGE_SHIFT)))
> return -EINVAL;
DIV_ROUND_UP is enough, neither arguments are unsigned long long
> @@ -494,7 +494,7 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
> goto out_unlock;
> }
> if (xen_feature(XENFEAT_auto_translated_physmap)) {
> - ret = alloc_empty_pages(vma, m.num);
> + ret = alloc_empty_pages(vma, nr_pages);
> if (ret < 0)
> goto out_unlock;
> } else
> @@ -518,6 +518,7 @@ static long privcmd_ioctl_mmap_batch(void __user *udata, int version)
> state.global_error = 0;
> state.version = version;
>
> + BUILD_BUG_ON(((PAGE_SIZE / sizeof(xen_pfn_t)) % XEN_PFN_PER_PAGE) != 0);
> /* mmap_batch_fn guarantees ret == 0 */
> BUG_ON(traverse_pages_block(m.num, sizeof(xen_pfn_t),
> &pagelist, mmap_batch_fn, &state));
> @@ -582,12 +583,13 @@ static void privcmd_close(struct vm_area_struct *vma)
> {
> struct page **pages = vma->vm_private_data;
> int numpgs = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> + int nr_pfn = (vma->vm_end - vma->vm_start) >> XEN_PAGE_SHIFT;
> int rc;
>
> if (!xen_feature(XENFEAT_auto_translated_physmap) || !numpgs || !pages)
> return;
>
> - rc = xen_unmap_domain_mfn_range(vma, numpgs, pages);
> + rc = xen_unmap_domain_mfn_range(vma, nr_pfn, pages);
> if (rc == 0)
> free_xenballooned_pages(numpgs, pages);
If you intend to pass the number of xen pages as nr argument to
xen_unmap_domain_mfn_range, then I think that the changes to
xen_xlate_unmap_gfn_range below are wrong.
> else
> diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c
> index 58a5389..1fac17c 100644
> --- a/drivers/xen/xlate_mmu.c
> +++ b/drivers/xen/xlate_mmu.c
> @@ -38,31 +38,9 @@
> #include <xen/interface/xen.h>
> #include <xen/interface/memory.h>
>
> -/* map fgmfn of domid to lpfn in the current domain */
> -static int map_foreign_page(unsigned long lpfn, unsigned long fgmfn,
> - unsigned int domid)
> -{
> - int rc;
> - struct xen_add_to_physmap_range xatp = {
> - .domid = DOMID_SELF,
> - .foreign_domid = domid,
> - .size = 1,
> - .space = XENMAPSPACE_gmfn_foreign,
> - };
> - xen_ulong_t idx = fgmfn;
> - xen_pfn_t gpfn = lpfn;
> - int err = 0;
> -
> - set_xen_guest_handle(xatp.idxs, &idx);
> - set_xen_guest_handle(xatp.gpfns, &gpfn);
> - set_xen_guest_handle(xatp.errs, &err);
> -
> - rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp);
> - return rc < 0 ? rc : err;
> -}
> -
> struct remap_data {
> xen_pfn_t *fgmfn; /* foreign domain's gmfn */
> + xen_pfn_t *efgmfn; /* pointer to the end of the fgmfn array */
> pgprot_t prot;
> domid_t domid;
> struct vm_area_struct *vma;
> @@ -71,24 +49,75 @@ struct remap_data {
> struct xen_remap_mfn_info *info;
> int *err_ptr;
> int mapped;
> +
> + /* Hypercall parameters */
> + int h_errs[XEN_PFN_PER_PAGE];
> + xen_ulong_t h_idxs[XEN_PFN_PER_PAGE];
> + xen_pfn_t h_gpfns[XEN_PFN_PER_PAGE];
I don't think you should be adding these fields to struct remap_data:
struct remap_data is used to pass multi pages arguments from
xen_xlate_remap_gfn_array to remap_pte_fn.
I think you need to introduce a different struct to pass per linux page
arguments from remap_pte_fn to setup_hparams.
> + int h_iter; /* Iterator */
> };
>
> +static int setup_hparams(struct page *page, unsigned long pfn, void *data)
> +{
> + struct remap_data *info = data;
> +
> + /* We may not have enough domain's gmfn to fill a Linux Page */
> + if (info->fgmfn == info->efgmfn)
> + return 0;
> +
> + info->h_idxs[info->h_iter] = *info->fgmfn;
> + info->h_gpfns[info->h_iter] = pfn;
> + info->h_errs[info->h_iter] = 0;
> + info->h_iter++;
> +
> + info->fgmfn++;
> +
> + return 0;
> +}
> +
> static int remap_pte_fn(pte_t *ptep, pgtable_t token, unsigned long addr,
> void *data)
> {
> struct remap_data *info = data;
> struct page *page = info->pages[info->index++];
> - unsigned long pfn = page_to_pfn(page);
> - pte_t pte = pte_mkspecial(pfn_pte(pfn, info->prot));
> + pte_t pte = pte_mkspecial(pfn_pte(page_to_pfn(page), info->prot));
> int rc;
> + uint32_t i;
> + struct xen_add_to_physmap_range xatp = {
> + .domid = DOMID_SELF,
> + .foreign_domid = info->domid,
> + .space = XENMAPSPACE_gmfn_foreign,
> + };
>
> - rc = map_foreign_page(pfn, *info->fgmfn, info->domid);
> - *info->err_ptr++ = rc;
> - if (!rc) {
> - set_pte_at(info->vma->vm_mm, addr, ptep, pte);
> - info->mapped++;
> + info->h_iter = 0;
> +
> + /* setup_hparams guarantees ret == 0 */
> + BUG_ON(xen_apply_to_page(page, setup_hparams, info));
> +
> + set_xen_guest_handle(xatp.idxs, info->h_idxs);
> + set_xen_guest_handle(xatp.gpfns, info->h_gpfns);
> + set_xen_guest_handle(xatp.errs, info->h_errs);
> + xatp.size = info->h_iter;
> +
> + rc = HYPERVISOR_memory_op(XENMEM_add_to_physmap_range, &xatp);
I would have thought that XENMEM_add_to_physmap_range operates at 4K
granularity, regardless of how the guest decides to layout its
pagetables. If so, the call to XENMEM_add_to_physmap_range needs to be
moved within the function passed to xen_apply_to_page.
> + /* info->err_ptr expect to have one error status per Xen PFN */
> + for (i = 0; i < info->h_iter; i++) {
> + int err = (rc < 0) ? rc : info->h_errs[i];
> +
> + *(info->err_ptr++) = err;
> + if (!err)
> + info->mapped++;
> }
> - info->fgmfn++;
> +
> + /*
> + * Note: The hypercall will return 0 in most of the case if even if
^ in most cases
> + * all the fgmfn are not mapped. We still have to update the pte
^ not all the fgmfn are mapped.
> + * as the userspace may decide to continue.
> + */
> + if (!rc)
> + set_pte_at(info->vma->vm_mm, addr, ptep, pte);
>
> return 0;
> }
> @@ -102,13 +131,14 @@ int xen_xlate_remap_gfn_array(struct vm_area_struct *vma,
> {
> int err;
> struct remap_data data;
> - unsigned long range = nr << PAGE_SHIFT;
> + unsigned long range = round_up(nr, XEN_PFN_PER_PAGE) << XEN_PAGE_SHIFT;
If would just BUG_ON(nr % XEN_PFN_PER_PAGE) and avoid the round_up;
> /* Kept here for the purpose of making sure code doesn't break
> x86 PVOPS */
> BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_IO)) == (VM_PFNMAP | VM_IO)));
>
> data.fgmfn = mfn;
> + data.efgmfn = mfn + nr;
If we assume that nr is a multiple of XEN_PFN_PER_PAGE, then we can get
rid of efgmfn.
> data.prot = prot;
> data.domid = domid;
> data.vma = vma;
> @@ -123,21 +153,38 @@ int xen_xlate_remap_gfn_array(struct vm_area_struct *vma,
> }
> EXPORT_SYMBOL_GPL(xen_xlate_remap_gfn_array);
>
> +static int unmap_gfn(struct page *page, unsigned long pfn, void *data)
> +{
> + int *nr = data;
> + struct xen_remove_from_physmap xrp;
> +
> + /* The Linux Page may not have been fully mapped to Xen */
> + if (!*nr)
> + return 0;
> +
> + xrp.domid = DOMID_SELF;
> + xrp.gpfn = pfn;
> + (void)HYPERVISOR_memory_op(XENMEM_remove_from_physmap, &xrp);
> +
> + (*nr)--;
I don't understand why you are passing nr as private argument. I would
just call XENMEM_remove_from_physmap unconditionally here. Am I missing
something? After all XENMEM_remove_from_physmap is just unmapping
at 4K granularity, right?
> + return 0;
> +}
> +
> int xen_xlate_unmap_gfn_range(struct vm_area_struct *vma,
> int nr, struct page **pages)
> {
> int i;
> + int nr_page = round_up(nr, XEN_PFN_PER_PAGE);
If nr is the number of xen pages, then this should be:
int nr_pages = DIV_ROUND_UP(nr, XEN_PFN_PER_PAGE);
> - for (i = 0; i < nr; i++) {
> - struct xen_remove_from_physmap xrp;
> - unsigned long pfn;
> + for (i = 0; i < nr_page; i++) {
> + /* unmap_gfn guarantees ret == 0 */
> + BUG_ON(xen_apply_to_page(pages[i], unmap_gfn, &nr));
> + }
>
> - pfn = page_to_pfn(pages[i]);
> + /* We should have consume every xen page */
^ consumed
> + BUG_ON(nr != 0);
>
> - xrp.domid = DOMID_SELF;
> - xrp.gpfn = pfn;
> - (void)HYPERVISOR_memory_op(XENMEM_remove_from_physmap, &xrp);
> - }
> return 0;
> }
> EXPORT_SYMBOL_GPL(xen_xlate_unmap_gfn_range);
> --
> 2.1.4
>
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