[Xen-devel] [PATCH v4] x86: add p2m_mmio_write_dm

[Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>]

XenGT (Intel Graphics Virtualization technology, please refer to
https://01.org/xen/blogs/srclarkx/2013/graphics-virtualization-
xengt) driver runs inside Dom0 as a virtual graphics device model,
and needs to trap and emulate the guest's write operations to some
specific memory pages, like memory pages used by guest graphics
driver as PPGTT(per-process graphics translation table). We agreed
to add a new p2m type "p2m_mmio_write_dm" to trap the write operation
on these graphic page tables.

Handling of this new p2m type are similar with existing p2m_ram_ro
in most condition checks, with only difference on final policy of
emulation vs. drop. For p2m_mmio_write_dm type pages, writes will
go to the device model via ioreq-server.

Previously, the conclusion in our v3 patch review is to provide a
more generalized HVMOP_map_io_range_to_ioreq_server hypercall, by
seperating rangesets inside a ioreq server to read-protected/write-
protected/both-prtected. Yet, after offline discussion with Paul,
we believe a more simplified solution may suffice. We can keep the
existing HVMOP_map_io_range_to_ioreq_server hypercall, and let the
user decide whether or not a p2m type change is necessary, because
in most cases the emulator will already use the p2m_mmio_dm type.

Changes from v3:
 - Use the existing HVMOP_map_io_range_to_ioreq_server hypercall
   to add write protected range.
 - Modify the HVMOP_set_mem_type hypercall to support the new p2m
   type for this range

Changes from v2:
 - Remove excute attribute of the new p2m type p2m_mmio_write_dm
 - Use existing rangeset for keeping the write protection page range
   instead of introducing hash table.
 - Some code style fix.

Changes from v1:
 - Changes the new p2m type name from p2m_ram_wp to p2m_mmio_write_dm.
   This means that we treat the pages as a special mmio range instead
   of ram.
 - Move macros to c file since only this file is using them.
 - Address various comments from Jan.

Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Wei Ye <wei.ye@xxxxxxxxx>
---
 xen/arch/x86/hvm/hvm.c          | 13 ++++++++++---
 xen/arch/x86/mm/p2m-ept.c       |  1 +
 xen/arch/x86/mm/p2m-pt.c        |  1 +
 xen/include/asm-x86/p2m.h       |  1 +
 xen/include/public/hvm/hvm_op.h |  1 +
 5 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 8f49b44..5f806e8 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2838,7 +2838,8 @@ int hvm_hap_nested_page_fault(paddr_t gpa, unsigned long 
gla,
      * to the mmio handler.
      */
     if ( (p2mt == p2m_mmio_dm) || 
-         (npfec.write_access && (p2mt == p2m_ram_ro)) )
+         (npfec.write_access &&
+               ((p2mt == p2m_ram_ro) || (p2mt == p2m_mmio_write_dm))) )
     {
         put_gfn(p2m->domain, gfn);
 
@@ -5922,6 +5923,8 @@ long do_hvm_op(unsigned long op, 
XEN_GUEST_HANDLE_PARAM(void) arg)
                 a.mem_type =  HVMMEM_ram_rw;
             else if ( p2m_is_grant(t) )
                 a.mem_type =  HVMMEM_ram_rw;
+            else if ( t == p2m_mmio_write_dm )
+                a.mem_type = HVMMEM_mmio_write_dm;
             else
                 a.mem_type =  HVMMEM_mmio_dm;
             rc = __copy_to_guest(arg, &a, 1) ? -EFAULT : 0;
@@ -5941,7 +5944,8 @@ long do_hvm_op(unsigned long op, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         static const p2m_type_t memtype[] = {
             [HVMMEM_ram_rw]  = p2m_ram_rw,
             [HVMMEM_ram_ro]  = p2m_ram_ro,
-            [HVMMEM_mmio_dm] = p2m_mmio_dm
+            [HVMMEM_mmio_dm] = p2m_mmio_dm,
+            [HVMMEM_mmio_write_dm] = p2m_mmio_write_dm
         };
 
         if ( copy_from_guest(&a, arg, 1) )
@@ -5987,14 +5991,17 @@ long do_hvm_op(unsigned long op, 
XEN_GUEST_HANDLE_PARAM(void) arg)
                 rc = -EAGAIN;
                 goto param_fail4;
             }
+
             if ( !p2m_is_ram(t) &&
-                 (!p2m_is_hole(t) || a.hvmmem_type != HVMMEM_mmio_dm) )
+                 (!p2m_is_hole(t) || a.hvmmem_type != HVMMEM_mmio_dm) &&
+                 t != p2m_mmio_write_dm )
             {
                 put_gfn(d, pfn);
                 goto param_fail4;
             }
 
             rc = p2m_change_type_one(d, pfn, t, memtype[a.hvmmem_type]);
+
             put_gfn(d, pfn);
             if ( rc )
                 goto param_fail4;
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index 15c6e83..e21a92d 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -136,6 +136,7 @@ static void ept_p2m_type_to_flags(ept_entry_t *entry, 
p2m_type_t type, p2m_acces
             entry->x = 0;
             break;
         case p2m_grant_map_ro:
+        case p2m_mmio_write_dm:
             entry->r = 1;
             entry->w = entry->x = 0;
             break;
diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
index e48b63a..26fb18d 100644
--- a/xen/arch/x86/mm/p2m-pt.c
+++ b/xen/arch/x86/mm/p2m-pt.c
@@ -94,6 +94,7 @@ static unsigned long p2m_type_to_flags(p2m_type_t t, mfn_t 
mfn)
     default:
         return flags | _PAGE_NX_BIT;
     case p2m_grant_map_ro:
+    case p2m_mmio_write_dm:
         return flags | P2M_BASE_FLAGS | _PAGE_NX_BIT;
     case p2m_ram_ro:
     case p2m_ram_logdirty:
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 5f7fe71..a7a45af 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -72,6 +72,7 @@ typedef enum {
     p2m_ram_shared = 12,          /* Shared or sharable memory */
     p2m_ram_broken = 13,          /* Broken page, access cause domain crash */
     p2m_map_foreign  = 14,        /* ram pages from foreign domain */
+    p2m_mmio_write_dm = 15,       /* Read-only; writes go to the device model 
*/
 } p2m_type_t;
 
 /* Modifiers to the query */
diff --git a/xen/include/public/hvm/hvm_op.h b/xen/include/public/hvm/hvm_op.h
index eeb0a60..a4e5345 100644
--- a/xen/include/public/hvm/hvm_op.h
+++ b/xen/include/public/hvm/hvm_op.h
@@ -81,6 +81,7 @@ typedef enum {
     HVMMEM_ram_rw,             /* Normal read/write guest RAM */
     HVMMEM_ram_ro,             /* Read-only; writes are discarded */
     HVMMEM_mmio_dm,            /* Reads and write go to the device model */
+    HVMMEM_mmio_write_dm       /* Read-only; writes go to the device model */
 } hvmmem_type_t;
 
 /* Following tools-only interfaces may change in future. */
-- 
1.9.1


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