Re: [PATCH] xen/virtio: Convert PAGE_SIZE/PAGE_SHIFT/PFN_UP to Xen counterparts
From: Xenia Ragiadakou
Date: Fri Oct 07 2022 - 11:50:49 EST
On 10/7/22 16:43, Oleksandr Tyshchenko wrote:
On 07.10.22 10:15, Xenia Ragiadakou wrote:
On 10/7/22 00:13, Oleksandr Tyshchenko wrote:
Hi Oleksandr
Hello Xenia
On 06.10.22 20:59, Xenia Ragiadakou wrote:
Hello Xenia
On 10/6/22 15:09, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Although XEN_PAGE_SIZE is equal to PAGE_SIZE (4KB) for now, it would
be more correct to use Xen specific #define-s as XEN_PAGE_SIZE can
be changed at some point in the future.
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
---
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
As it was proposed at:
https://urldefense.com/v3/__https://lore.kernel.org/xen-devel/20221005174823.1800761-1-olekstysh@xxxxxxxxx/__;!!GF_29dbcQIUBPA!zHt-xZ_7tZc_EM6zva21E_YgwIiEeimFWfsJIpPwAu-TBcnzQhXHqlKzmXmwIcI6uIx_arHNZiaZeHt_428_8p-DyMpd$
[lore[.]kernel[.]org]
Should go in only after that series.
---
drivers/xen/grant-dma-ops.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index c66f56d24013..5392fdc25dca 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -31,12 +31,12 @@ static DEFINE_XARRAY_FLAGS(xen_grant_dma_devices,
XA_FLAGS_LOCK_IRQ);
static inline dma_addr_t grant_to_dma(grant_ref_t grant)
{
- return XEN_GRANT_DMA_ADDR_OFF | ((dma_addr_t)grant <<
PAGE_SHIFT);
+ return XEN_GRANT_DMA_ADDR_OFF | ((dma_addr_t)grant <<
XEN_PAGE_SHIFT);
}
With this change, can the offset added to the dma handle, generated by
grant_to_dma(), be the offset in the page? Couldn't it corrupt the
grant ref?
Good point, indeed, I think it could corrupt if guest uses a different
than Xen page granularity (i.e 64KB).
static inline grant_ref_t dma_to_grant(dma_addr_t dma)
{
- return (grant_ref_t)((dma & ~XEN_GRANT_DMA_ADDR_OFF) >>
PAGE_SHIFT);
+ return (grant_ref_t)((dma & ~XEN_GRANT_DMA_ADDR_OFF) >>
XEN_PAGE_SHIFT);
}
static struct xen_grant_dma_data *find_xen_grant_dma_data(struct
device *dev)
@@ -79,7 +79,7 @@ static void *xen_grant_dma_alloc(struct device
*dev, size_t size,
unsigned long attrs)
{
struct xen_grant_dma_data *data;
- unsigned int i, n_pages = PFN_UP(size);
+ unsigned int i, n_pages = XEN_PFN_UP(size);
unsigned long pfn;
grant_ref_t grant;
void *ret;
@@ -91,14 +91,14 @@ static void *xen_grant_dma_alloc(struct device
*dev, size_t size,
if (unlikely(data->broken))
return NULL;
- ret = alloc_pages_exact(n_pages * PAGE_SIZE, gfp);
+ ret = alloc_pages_exact(n_pages * XEN_PAGE_SIZE, gfp);
if (!ret)
return NULL;
pfn = virt_to_pfn(ret);
if (gnttab_alloc_grant_reference_seq(n_pages, &grant)) {
- free_pages_exact(ret, n_pages * PAGE_SIZE);
+ free_pages_exact(ret, n_pages * XEN_PAGE_SIZE);
return NULL;
}
@@ -116,7 +116,7 @@ static void xen_grant_dma_free(struct device
*dev, size_t size, void *vaddr,
dma_addr_t dma_handle, unsigned long attrs)
{
struct xen_grant_dma_data *data;
- unsigned int i, n_pages = PFN_UP(size);
+ unsigned int i, n_pages = XEN_PFN_UP(size);
grant_ref_t grant;
data = find_xen_grant_dma_data(dev);
@@ -138,7 +138,7 @@ static void xen_grant_dma_free(struct device
*dev, size_t size, void *vaddr,
gnttab_free_grant_reference_seq(grant, n_pages);
- free_pages_exact(vaddr, n_pages * PAGE_SIZE);
+ free_pages_exact(vaddr, n_pages * XEN_PAGE_SIZE);
}
static struct page *xen_grant_dma_alloc_pages(struct device *dev,
size_t size,
@@ -168,7 +168,7 @@ static dma_addr_t xen_grant_dma_map_page(struct
device *dev, struct page *page,
unsigned long attrs)
{
struct xen_grant_dma_data *data;
- unsigned int i, n_pages = PFN_UP(offset + size);
+ unsigned int i, n_pages = XEN_PFN_UP(offset + size);
The offset, here, refers to the offset in the page ...
grant_ref_t grant;
dma_addr_t dma_handle;
@@ -200,8 +200,8 @@ static void xen_grant_dma_unmap_page(struct
device *dev, dma_addr_t dma_handle,
unsigned long attrs)
{
struct xen_grant_dma_data *data;
- unsigned long offset = dma_handle & (PAGE_SIZE - 1);
- unsigned int i, n_pages = PFN_UP(offset + size);
+ unsigned long offset = dma_handle & ~XEN_PAGE_MASK;
... while, here, it refers to the offset in the grant.
So, the calculated number of grants may differ.
Good point, I think you are right, so we need to additionally use
xen_offset_in_page() macro in xen_grant_dma_map_page(),
something like that to be squashed with current patch:
diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
index 9d5eca6d638a..bb984dc05deb 100644
--- a/drivers/xen/grant-dma-ops.c
+++ b/drivers/xen/grant-dma-ops.c
@@ -169,7 +169,7 @@ static dma_addr_t xen_grant_dma_map_page(struct
device *dev, struct page *page,
unsigned long attrs)
{
struct xen_grant_dma_data *data;
- unsigned int i, n_pages = XEN_PFN_UP(offset + size);
+ unsigned int i, n_pages = XEN_PFN_UP(xen_offset_in_page(offset)
+ size);
grant_ref_t grant;
dma_addr_t dma_handle;
@@ -191,7 +191,7 @@ static dma_addr_t xen_grant_dma_map_page(struct
device *dev, struct page *page,
xen_page_to_gfn(page) + i, dir ==
DMA_TO_DEVICE);
}
- dma_handle = grant_to_dma(grant) + offset;
+ dma_handle = grant_to_dma(grant) + xen_offset_in_page(offset);
return dma_handle;
}
Did I get your point right?
I think it 's more complicated than that.
Let's say that the offset in page is > XEN_PAGE_SIZE, then the
calculation of the number of grants won't take into account the part
of the offset that is multiple of the XEN_PAGE_SIZE i.e it will
calculate only the strictly necessary number of grants.
But xen_grant_dma_map_page() grants access to the whole page because,
as it can be observed in the code snippet below, it does not take into
account the page offset.
for (i = 0; i < n_pages; i++) {
gnttab_grant_foreign_access_ref(grant + i, data->backend_domid,
xen_page_to_gfn(page) + i, dir == DMA_TO_DEVICE);
}
Thanks, valid point. Agree it's indeed more complicated. I will comment
on that later. I have just pushed another fix, it is not related to
XEN_PAGE_SIZE directly, but also about page offset > PAGE_SIZE
I got a little bit confused with the order that the patches will be
applied :)
IIUC the above scenario cannot happen, i.e the offset to be > PAGE_SIZE,
because this callback is used to map for transfer a portion of a single
page.
so touches the same code and should be prereq:
https://lore.kernel.org/all/20221007132736.2275574-1-olekstysh@xxxxxxxxx/
+ unsigned int i, n_pages = XEN_PFN_UP(offset + size);
grant_ref_t grant;
if (WARN_ON(dir == DMA_NONE))
Thank you.
--
Xenia