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Re: [Xen-devel] RT Xen on ARM - R-Car series


On 2/4/19 12:53 PM, Roger Pau Monné wrote:
On Fri, Feb 01, 2019 at 05:40:14PM +0000, Julien Grall wrote:

On 01/02/2019 16:53, Roger Pau Monné wrote:
On Thu, Jan 31, 2019 at 11:14:37PM +0000, Julien Grall wrote:
On 1/31/19 9:56 PM, Stefano Stabellini wrote:
On Thu, 31 Jan 2019, Julien Grall wrote:
On 31/01/2019 12:00, Andrii Anisov wrote:
On 31.01.19 13:37, Julien Grall wrote:
So, I've got a hacky patch to 'fix' this on x86, by taking a reference
to the mfn behind the virtual address provided when setting up the
hypercall and mapping it in Xen.

That was the idea I had in mind :). Hopefully, no guest is modifying the
mapping (i.e the virtual address point to a different physical address)

This however doesn't work on ARM due
to the lack of paging_gva_to_gfn. I guess there's something similar to
translate a guest virtual address into a gfn or a mfn?

get_page_from_gva should to the job for you.
+int map_runstate_area(struct vcpu *v,
+                      struct vcpu_register_runstate_memory_area *area)
+    unsigned long offset;
+    unsigned int i;
+    struct domain *d = v->domain;
+    size_t size =
+        has_32bit_shinfo((v)->domain) ? sizeof(*v->compat_runstate_guest) :
+                                        sizeof(*v->runstate_guest);
+    if ( v->runstate_guest )
+    {
+        return -EBUSY;
+    }
+    offset = area->addr.p & ~PAGE_MASK;
+    for ( i = 0; i < ARRAY_SIZE(v->runstate_mfn); i++ )
+    {
+        p2m_type_t t;
+        uint32_t pfec = PFEC_page_present;
+        gfn_t gfn = _gfn(paging_gva_to_gfn(v, area->addr.p, &pfec));
+        struct page_info *pg;
+        if ( gfn_eq(gfn, INVALID_GFN) )
+            return -EFAULT;
+        v->runstate_mfn[i] = get_gfn(d, gfn_x(gfn), &t);

get_gfn would need to be implemented on Arm.

+        if ( t != p2m_ram_rw || mfn_eq(v->runstate_mfn[i], INVALID_MFN) )
+            return -EFAULT;
+        pg = mfn_to_page(v->runstate_mfn[i]);
+        if ( !pg || !get_page_type(pg, PGT_writable_page) )
+        {
+            put_gfn(d, gfn_x(gfn));
+            return -EFAULT;
+        }
+        put_gfn(d, gfn_x(gfn));
+        if ( PFN_DOWN(gfn_x(gfn) + size) == PFN_DOWN(gfn_x(gfn)) )

This looks wrong, you seem to mix address and frame. I think you might want:

if ( gfn_eq(gfn_add(gfn, PFN_DOWN(size)), gfn) )


Here is an updated version which seems to build on ARM. I don't have
an easy way to test this, could you give it a spin?

Thank you for writing a patch. I am back in France this week for family reason and will not have time properly give a spin this week. Stefano, Andrii, can you test it?

I don't like adding CONFIG_X86/ARM in common code, so it might be
worth to either try to factor this out into arch specific code, or
even better, provide common functions to translate a guest virtual
address into a gfn, mfn or page.

I would prefer GVA to MFN/page because we already have a fairly complicate helper handling all the cases (e.g memaccess, break-before-make, ...) for translation and taking a reference on the page. Although we could potentially split the function in two if we want to cater any other translation.

One comment below.

+#elif defined(CONFIG_ARM)
+        pg = get_page_from_gva(v, area->addr.p, GV2M_WRITE);
+        if ( !pg || !get_page_type(pg, PGT_writable_page) )

One reference is already taken by get_page_from_gva. So you should not need to take another here.


Julien Grall

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