[Xen-devel] [PATCH v3] x86: clarify shadow paging Dom0 support

[Wei Liu <wei.liu2@xxxxxxxxxx>]

Classic PV shadow paging Dom0 has been broken for years, and can't
possibly be configured after 4045953.

PVH shadow paging Dom0 should still be possible.

Change the code and documentation to clarify that.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
v3:
1. don't panic

v2:
1. simplify need_paging
2. move panic to construct_dom0

Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 docs/misc/xen-command-line.markdown |  8 ++------
 xen/arch/x86/dom0_build.c           | 11 ++++++++---
 xen/arch/x86/pv/dom0_build.c        |  5 -----
 3 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index bdbdb8a53b..9eb85d68b5 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -652,11 +652,6 @@ restrictions set up here. Note that the values to be 
specified here are
 ACPI PXM ones, not Xen internal node numbers. `relaxed` sets up vCPU
 affinities to prefer but be not limited to the specified node(s).
 
-### dom0\_shadow
-> `= <boolean>`
-
-This option is deprecated, please use `dom0=shadow` instead.
-
 ### dom0\_vcpus\_pin
 > `= <boolean>`
 
@@ -679,7 +674,8 @@ Flag that makes a dom0 boot in PVHv2 mode.
 
 > Default: `false`
 
-Flag that makes a dom0 use shadow paging.
+Flag that makes a dom0 use shadow paging. Only works when "pvh" is
+enabled.
 
 ### dtuart (ARM)
 > `= path [:options]`
diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index 20221b5e32..8597d43b11 100644
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -174,7 +174,6 @@ struct vcpu *__init alloc_dom0_vcpu0(struct domain *dom0)
 
 #ifdef CONFIG_SHADOW_PAGING
 bool __initdata opt_dom0_shadow;
-boolean_param("dom0_shadow", opt_dom0_shadow);
 #endif
 bool __initdata dom0_pvh;
 
@@ -252,8 +251,8 @@ unsigned long __init dom0_compute_nr_pages(
             avail -= max_pdx >> s;
     }
 
-    need_paging = is_hvm_domain(d) ? !iommu_hap_pt_share || !paging_mode_hap(d)
-                                   : opt_dom0_shadow;
+    need_paging = is_hvm_domain(d) &&
+        (!iommu_hap_pt_share || !paging_mode_hap(d));
     for ( ; ; need_paging = 0 )
     {
         nr_pages = dom0_nrpages;
@@ -456,6 +455,12 @@ int __init construct_dom0(struct domain *d, const module_t 
*image,
 
     process_pending_softirqs();
 
+    if ( opt_dom0_shadow && !dom0_pvh )
+    {
+        opt_dom0_shadow = false;
+        printk("Shadow Dom0 requires PVH. Option ignored.");
+    }
+
     return (is_hvm_domain(d) ? dom0_construct_pvh : dom0_construct_pv)
            (d, image, image_headroom, initrd,bootstrap_map, cmdline);
 }
diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 65cd2c5019..18c19a256f 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -870,11 +870,6 @@ int __init dom0_construct_pv(struct domain *d,
     regs->rsi = vstartinfo_start;
     regs->eflags = X86_EFLAGS_IF;
 
-#ifdef CONFIG_SHADOW_PAGING
-    if ( opt_dom0_shadow && paging_enable(d, PG_SH_enable) == 0 )
-        paging_update_paging_modes(v);
-#endif
-
     if ( test_bit(XENFEAT_supervisor_mode_kernel, parms.f_required) )
         panic("Dom0 requires supervisor-mode execution");
 
-- 
2.11.0


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