x86/dom0: attempt to fixup p2m page-faults for PVH dom0

When building a PVH dom0 Xen attempts to map all (relevant) MMIO regions
into the p2m for dom0 access.  However the information Xen has about the
host memory map is limited.  Xen doesn't have access to any resources
described in ACPI dynamic tables, and hence the p2m mappings provided might
not be complete.

PV doesn't suffer from this issue because a PV dom0 is capable of mapping
into it's page-tables any address not explicitly banned in d->iomem_caps.

Introduce a new command line options that allows Xen to attempt to fixup
the p2m page-faults, by creating p2m identity maps in response to p2m
page-faults.

This is aimed as a workaround to small ACPI regions Xen doesn't know about.
Note that missing large MMIO regions mapped in this way will lead to
slowness due to the VM exit processing, plus the mappings will always use
small pages.

The ultimate aim is to attempt to bring better parity with a classic PV
dom0.

Note such fixup rely on the CPU doing the access to the unpopulated
address.  If the access is attempted from a device instead there's no
possible way to fixup, as IOMMU page-fault are asynchronous.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
---
Only slightly tested on my local PVH dom0 deployment.
---
Changes since v1:
 - Make the fixup function static.
 - Print message in case mapping already exists.

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 04c21d5bcea48c3b6ad2fa2db0e8b3d60574ce00..e99c5a55157a413be43c8dc4e4f9e2501f75760d 100644 (file)
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Changed
 
 ### Added
+ - On x86:
+   - Option to attempt to fixup p2m page-faults on PVH dom0.
 
 ### Removed
 

diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index 0c6225391d55c34ebbd909dd8618ea37398a20a0..7e0f81adabb14f4acfcb2b3af44907bccc5ddd29 100644 (file)
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -822,7 +822,8 @@ Specify the bit width of the DMA heap.
 
 ### dom0
     = List of [ pv | pvh, shadow=<bool>, verbose=<bool>,
-                cpuid-faulting=<bool>, msr-relaxed=<bool> ] (x86)
+                cpuid-faulting=<bool>, msr-relaxed=<bool>,
+                pf-fixup=<bool> ] (x86)
 
     = List of [ sve=<integer> ] (Arm64)
 
@@ -883,6 +884,19 @@ Controls for how dom0 is constructed on x86 systems.
 
     If using this option is necessary to fix an issue, please report a bug.
 
+*   The `pf-fixup` boolean is only applicable when using a PVH dom0 and
+    defaults to false.
+
+    When running dom0 in PVH mode the dom0 kernel has no way to map MMIO
+    regions into its physical memory map, such mode relies on Xen dom0 builder
+    populating the physical memory map with all MMIO regions that dom0 should
+    access.  However Xen doesn't have a complete picture of the host memory
+    map, due to not being able to process ACPI dynamic tables.
+
+    The `pf-fixup` option allows Xen to attempt to add missing MMIO regions
+    to the dom0 physical memory map in response to page-faults generated by
+    dom0 trying to access unpopulated entries in the memory map.
+
 Enables features on dom0 on Arm systems.
 
 *   The `sve` integer parameter enables Arm SVE usage for Dom0 and sets the

diff --git a/xen/arch/x86/dom0_build.c b/xen/arch/x86/dom0_build.c
index e8f5bf5447bc47a6daa3d95787106a4c11e80d31..3b9681dc913415a5d3b73801a85cef8eaf39d822 100644 (file)
--- a/xen/arch/x86/dom0_build.c
+++ b/xen/arch/x86/dom0_build.c
@@ -16,6 +16,7 @@
 #include <asm/dom0_build.h>
 #include <asm/guest.h>
 #include <asm/hpet.h>
+#include <asm/hvm/emulate.h>
 #include <asm/io-ports.h>
 #include <asm/io_apic.h>
 #include <asm/p2m.h>
@@ -286,6 +287,10 @@ int __init parse_arch_dom0_param(const char *s, const char *e)
         opt_dom0_cpuid_faulting = val;
     else if ( (val = parse_boolean("msr-relaxed", s, e)) >= 0 )
         opt_dom0_msr_relaxed = val;
+#ifdef CONFIG_HVM
+    else if ( (val = parse_boolean("pf-fixup", s, e)) >= 0 )
+        opt_dom0_pf_fixup = val;
+#endif
     else
         return -EINVAL;
 

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 08b9493e6d88e46aba15b0eff61dbbb8e0910e20..3cd7f2e22f269ebe302170de798852176172defd 100644 (file)
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -10,12 +10,15 @@
  */
 
 #include <xen/init.h>
+#include <xen/iocap.h>
 #include <xen/ioreq.h>
 #include <xen/lib.h>
 #include <xen/sched.h>
 #include <xen/paging.h>
 #include <xen/trace.h>
 #include <xen/vm_event.h>
+
+#include <asm/altp2m.h>
 #include <asm/event.h>
 #include <asm/i387.h>
 #include <asm/xstate.h>
@@ -161,6 +164,36 @@ void hvmemul_cancel(struct vcpu *v)
     hvmemul_cache_disable(v);
 }
 
+bool __ro_after_init opt_dom0_pf_fixup;
+static int hwdom_fixup_p2m(paddr_t addr)
+{
+    unsigned long gfn = paddr_to_pfn(addr);
+    struct domain *currd = current->domain;
+    p2m_type_t type;
+    mfn_t mfn;
+    int rc;
+
+    ASSERT(is_hardware_domain(currd));
+    ASSERT(!altp2m_active(currd));
+
+    /*
+     * Fixups are only applied for MMIO holes, and rely on the hardware domain
+     * having identity mappings for non RAM regions (gfn == mfn).
+     */
+    if ( !iomem_access_permitted(currd, gfn, gfn) ||
+         !is_memory_hole(_mfn(gfn), _mfn(gfn)) )
+        return -EPERM;
+
+    mfn = get_gfn(currd, gfn, &type);
+    if ( !mfn_eq(mfn, INVALID_MFN) || !p2m_is_hole(type) )
+        rc = mfn_eq(mfn, _mfn(gfn)) ? -EEXIST : -ENOTEMPTY;
+    else
+        rc = set_mmio_p2m_entry(currd, _gfn(gfn), _mfn(gfn), 0);
+    put_gfn(currd, gfn);
+
+    return rc;
+}
+
 static int hvmemul_do_io(
     bool is_mmio, paddr_t addr, unsigned long *reps, unsigned int size,
     uint8_t dir, bool df, bool data_is_addr, uintptr_t data)
@@ -338,8 +371,45 @@ static int hvmemul_do_io(
         if ( !s )
         {
             if ( is_mmio && is_hardware_domain(currd) )
-                gdprintk(XENLOG_DEBUG, "unhandled memory %s %#lx size %u\n",
-                         dir ? "read from" : "write to", addr, size);
+            {
+                /*
+                 * PVH dom0 is likely missing MMIO mappings on the p2m, due to
+                 * the incomplete information Xen has about the memory layout.
+                 *
+                 * Either print a message to note dom0 attempted to access an
+                 * unpopulated GPA, or try to fixup the p2m by creating an
+                 * identity mapping for the faulting GPA.
+                 */
+                if ( opt_dom0_pf_fixup )
+                {
+                    int inner_rc = hwdom_fixup_p2m(addr);
+
+                    if ( !inner_rc || inner_rc == -EEXIST )
+                    {
+                        if ( !inner_rc )
+                            gdprintk(XENLOG_DEBUG,
+                                     "fixup p2m mapping for page %lx added\n",
+                                     paddr_to_pfn(addr));
+                        else
+                            gprintk(XENLOG_INFO,
+                                    "fixup p2m mapping for page %lx already present\n",
+                                    paddr_to_pfn(addr));
+
+                        rc = X86EMUL_RETRY;
+                        vio->req.state = STATE_IOREQ_NONE;
+                        break;
+                    }
+
+                    gprintk(XENLOG_WARNING,
+                            "unable to fixup memory %s %#lx size %u: %d\n",
+                            dir ? "read from" : "write to", addr, size,
+                            inner_rc);
+                }
+                else
+                    gdprintk(XENLOG_DEBUG,
+                             "unhandled memory %s %#lx size %u\n",
+                             dir ? "read from" : "write to", addr, size);
+            }
             rc = hvm_process_io_intercept(&null_handler, &p);
             vio->req.state = STATE_IOREQ_NONE;
         }

diff --git a/xen/arch/x86/include/asm/hvm/emulate.h b/xen/arch/x86/include/asm/hvm/emulate.h
index 45b03e4e37bbcd5475f58252d4bde659dac4935e..d61eacfaa7792364074eae289a946d350377c757 100644 (file)
--- a/xen/arch/x86/include/asm/hvm/emulate.h
+++ b/xen/arch/x86/include/asm/hvm/emulate.h
@@ -148,6 +148,9 @@ static inline void hvmemul_write_cache(const struct vcpu *v, paddr_t gpa,
 void hvm_dump_emulation_state(const char *loglvl, const char *prefix,
                               struct hvm_emulate_ctxt *hvmemul_ctxt, int rc);
 
+/* For PVH dom0: signal whether to attempt fixup of p2m page-faults. */
+extern bool opt_dom0_pf_fixup;
+
 #endif /* __ASM_X86_HVM_EMULATE_H__ */
 
 /*