[Xen-changelog] [xen staging] x86/hvm: split all linear reads and writes at page boundary

[patchbot@xxxxxxx]

commit 2d527ba310dc6695bba2df118ff9e053f7e40c82
Author:     Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
AuthorDate: Mon Mar 18 16:28:45 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Mar 18 16:28:45 2019 +0100

    x86/hvm: split all linear reads and writes at page boundary
    
    Ruling out page straddling at linear level makes it easier to
    distinguish chunks that require proper handling as MMIO access
    and not complete them as page straddling memory transactions
    prematurely. This doesn't change the general behavior.
    
    Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/hvm/emulate.c | 70 +++++++++++++++++++++++++---------------------
 1 file changed, 38 insertions(+), 32 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 754baf68d5..c236e7da1f 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -1089,12 +1089,25 @@ static int linear_read(unsigned long addr, unsigned int 
bytes, void *p_data,
                        uint32_t pfec, struct hvm_emulate_ctxt *hvmemul_ctxt)
 {
     pagefault_info_t pfinfo;
-    int rc = hvm_copy_from_guest_linear(p_data, addr, bytes, pfec, &pfinfo);
+    unsigned int offset = addr & ~PAGE_MASK;
+    int rc;
 
-    switch ( rc )
+    if ( offset + bytes > PAGE_SIZE )
     {
-        unsigned int offset, part1;
+        unsigned int part1 = PAGE_SIZE - offset;
+
+        /* Split the access at the page boundary. */
+        rc = linear_read(addr, part1, p_data, pfec, hvmemul_ctxt);
+        if ( rc == X86EMUL_OKAY )
+            rc = linear_read(addr + part1, bytes - part1, p_data + part1,
+                             pfec, hvmemul_ctxt);
+        return rc;
+    }
+
+    rc = hvm_copy_from_guest_linear(p_data, addr, bytes, pfec, &pfinfo);
 
+    switch ( rc )
+    {
     case HVMTRANS_okay:
         return X86EMUL_OKAY;
 
@@ -1106,19 +1119,9 @@ static int linear_read(unsigned long addr, unsigned int 
bytes, void *p_data,
         if ( pfec & PFEC_insn_fetch )
             return X86EMUL_UNHANDLEABLE;
 
-        offset = addr & ~PAGE_MASK;
-        if ( offset + bytes <= PAGE_SIZE )
-            return hvmemul_linear_mmio_read(addr, bytes, p_data, pfec,
-                                            hvmemul_ctxt,
-                                            known_gla(addr, bytes, pfec));
-
-        /* Split the access at the page boundary. */
-        part1 = PAGE_SIZE - offset;
-        rc = linear_read(addr, part1, p_data, pfec, hvmemul_ctxt);
-        if ( rc == X86EMUL_OKAY )
-            rc = linear_read(addr + part1, bytes - part1, p_data + part1,
-                             pfec, hvmemul_ctxt);
-        return rc;
+        return hvmemul_linear_mmio_read(addr, bytes, p_data, pfec,
+                                        hvmemul_ctxt,
+                                        known_gla(addr, bytes, pfec));
 
     case HVMTRANS_gfn_paged_out:
     case HVMTRANS_gfn_shared:
@@ -1132,12 +1135,25 @@ static int linear_write(unsigned long addr, unsigned 
int bytes, void *p_data,
                         uint32_t pfec, struct hvm_emulate_ctxt *hvmemul_ctxt)
 {
     pagefault_info_t pfinfo;
-    int rc = hvm_copy_to_guest_linear(addr, p_data, bytes, pfec, &pfinfo);
+    unsigned int offset = addr & ~PAGE_MASK;
+    int rc;
 
-    switch ( rc )
+    if ( offset + bytes > PAGE_SIZE )
     {
-        unsigned int offset, part1;
+        unsigned int part1 = PAGE_SIZE - offset;
+
+        /* Split the access at the page boundary. */
+        rc = linear_write(addr, part1, p_data, pfec, hvmemul_ctxt);
+        if ( rc == X86EMUL_OKAY )
+            rc = linear_write(addr + part1, bytes - part1, p_data + part1,
+                              pfec, hvmemul_ctxt);
+        return rc;
+    }
+
+    rc = hvm_copy_to_guest_linear(addr, p_data, bytes, pfec, &pfinfo);
 
+    switch ( rc )
+    {
     case HVMTRANS_okay:
         return X86EMUL_OKAY;
 
@@ -1146,19 +1162,9 @@ static int linear_write(unsigned long addr, unsigned int 
bytes, void *p_data,
         return X86EMUL_EXCEPTION;
 
     case HVMTRANS_bad_gfn_to_mfn:
-        offset = addr & ~PAGE_MASK;
-        if ( offset + bytes <= PAGE_SIZE )
-            return hvmemul_linear_mmio_write(addr, bytes, p_data, pfec,
-                                             hvmemul_ctxt,
-                                             known_gla(addr, bytes, pfec));
-
-        /* Split the access at the page boundary. */
-        part1 = PAGE_SIZE - offset;
-        rc = linear_write(addr, part1, p_data, pfec, hvmemul_ctxt);
-        if ( rc == X86EMUL_OKAY )
-            rc = linear_write(addr + part1, bytes - part1, p_data + part1,
-                              pfec, hvmemul_ctxt);
-        return rc;
+        return hvmemul_linear_mmio_write(addr, bytes, p_data, pfec,
+                                         hvmemul_ctxt,
+                                         known_gla(addr, bytes, pfec));
 
     case HVMTRANS_gfn_paged_out:
     case HVMTRANS_gfn_shared:
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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