[Xen-changelog] [xen staging] x86/boot: Wire up dom0=shadow for PV dom0

[patchbot@xxxxxxx]

commit 8978d258bb455794aed521928b2cdf1e12098d73
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Sep 14 18:50:01 2018 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Thu May 23 15:59:00 2019 +0100

    x86/boot: Wire up dom0=shadow for PV dom0
    
    This would have been very handy when debugging some pv-l1tf issues.  As 
there
    is no cost to supporting it, wire it up.
    
    Due to the way dom0 is constructed, switching into shadow mode must be done
    after the pagetables are written, and because of partially being in dom0
    context, shadow_enable() doesn't like the state it finds.
    
    Reuse the pv_l1tf tasklet for convenience, which will switch dom0 into 
shadow
    mode just before it starts executing.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 docs/misc/xen-command-line.pandoc | 14 +++++++++-----
 xen/arch/x86/dom0_build.c         |  8 --------
 xen/arch/x86/pv/dom0_build.c      |  9 +++++++++
 3 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index 1fc18026bb..f53d5afb92 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -675,12 +675,16 @@ Controls for how dom0 is constructed on x86 systems.
         selected mode.
     *   For a PVH dom0, the hardware must have VT-x/SVM extensions available.
 
-*   The `shadow` boolean is only applicable when dom0 is constructed as a PVH
-    guest, and controls whether dom0 uses hardware assisted paging, or shadow
-    paging.  The default is HAP when available, and shadow otherwise.
+*   The `shadow` boolean allows dom0 to be explicitly constructed using shadow
+    paging.  This option is unavailable when `CONFIG_SHADOW_PAGING` is
+    disabled.
 
-    This option is unavailable when `CONFIG_SHADOW_PAGING` is disabled.  Such
-    builds of Xen require HAP-capable hardware to use a PVH dom0.
+    For PVH, dom0 defaults to using HAP on capable hardware, and falls back to
+    shadow paging otherwise.  A PVH dom0 cannot be used if Xen is compiled
+    without shadow paging support, and the hardware lacks HAP support.
+
+    For PV, the use of dom0 shadow mode is only for development purposes.  PV
+    guests do no require any paging support by default.
 
 *   The `verbose` boolean is intended for diagnostics, and prints out extra
     information during the dom0 build.  It defaults to false.
diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index 27315d5bd2..93e5531b8a 100644
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -588,14 +588,6 @@ int __init construct_dom0(struct domain *d, const module_t 
*image,
 
     process_pending_softirqs();
 
-#ifdef CONFIG_SHADOW_PAGING
-    if ( opt_dom0_shadow && !dom0_pvh )
-    {
-        opt_dom0_shadow = false;
-        printk(XENLOG_WARNING "Shadow Dom0 requires PVH. Option ignored.\n");
-    }
-#endif
-
     if ( is_hvm_domain(d) )
         rc = dom0_construct_pvh(d, image, image_headroom, initrd, cmdline);
     else if ( is_pv_domain(d) )
diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 064a10ed1f..4a1526ab2a 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -906,6 +906,15 @@ int __init dom0_construct_pv(struct domain *d,
     if ( d->domain_id == hardware_domid )
         iommu_hwdom_init(d);
 
+    /* Activate shadow mode, if requested.  Reuse the pv_l1tf tasklet. */
+#ifdef CONFIG_SHADOW_PAGING
+    if ( opt_dom0_shadow )
+    {
+        printk("Switching dom0 to using shadow paging\n");
+        tasklet_schedule(&d->arch.paging.shadow.pv_l1tf_tasklet);
+    }
+#endif
+
     v->is_initialised = 1;
     clear_bit(_VPF_down, &v->pause_flags);
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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