linux-kernel - [PATCH v2 5/7] xen: add capability to remap non-RAM pages to different PFNs

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Message-ID: <20240820082012.31316-6-jgross@suse.com>
Date: Tue, 20 Aug 2024 10:20:10 +0200
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org,
	x86@...nel.org
Cc: Juergen Gross <jgross@...e.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	xen-devel@...ts.xenproject.org
Subject: [PATCH v2 5/7] xen: add capability to remap non-RAM pages to different PFNs

When running as a Xen PV dom0 it can happen that the kernel is being
loaded to a guest physical address conflicting with the host memory
map.

In order to be able to resolve this conflict, add the capability to
remap non-RAM areas to different guest PFNs. A function to use this
remapping information for other purposes than doing the remap will be
added when needed.

As the number of conflicts should be rather low (currently only
machines with max. 1 conflict are known), save the remap data in a
small statically allocated array.

Signed-off-by: Juergen Gross <jgross@...e.com>
---
V2:
- split off from patch 5 of V1 of the series
- moved to p2m.c
---
 arch/x86/xen/p2m.c     | 65 ++++++++++++++++++++++++++++++++++++++++++
 arch/x86/xen/xen-ops.h |  3 ++
 2 files changed, 68 insertions(+)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 7c735b730acd..bb55e0fe1a04 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -80,6 +80,7 @@
 #include <asm/xen/hypervisor.h>
 #include <xen/balloon.h>
 #include <xen/grant_table.h>
+#include <xen/hvc-console.h>
 
 #include "xen-ops.h"
 
@@ -792,6 +793,70 @@ int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops,
 	return ret;
 }
 
+/* Remapped non-RAM areas */
+#define NR_NONRAM_REMAP 4
+static struct nonram_remap {
+	phys_addr_t maddr;
+	phys_addr_t paddr;
+	unsigned long size;
+} xen_nonram_remap[NR_NONRAM_REMAP];
+static unsigned int nr_nonram_remap;
+
+/*
+ * Do the real remapping of non-RAM regions as specified in the
+ * xen_nonram_remap[] array.
+ * In case of an error just crash the system.
+ */
+void __init xen_do_remap_nonram(void)
+{
+	unsigned int i;
+	unsigned int remapped = 0;
+	struct nonram_remap *remap = xen_nonram_remap;
+	unsigned long pfn, mfn, len;
+
+	if (!nr_nonram_remap)
+		return;
+
+	for (i = 0; i < nr_nonram_remap; i++) {
+		pfn = PFN_DOWN(remap->paddr);
+		mfn = PFN_DOWN(remap->maddr);
+		for (len = 0; len < remap->size; len += PAGE_SIZE) {
+			if (!set_phys_to_machine(pfn, mfn)) {
+				pr_err("Failed to set p2m mapping for pfn=%ld mfn=%ld\n",
+				       pfn, mfn);
+				BUG();
+			}
+
+			pfn++;
+			mfn++;
+			remapped++;
+		}
+
+		remap++;
+	}
+
+	pr_info("Remapped %u non-RAM page(s)\n", remapped);
+}
+
+/*
+ * Add a new non-RAM remap entry.
+ * In case of no free entry found, just crash the system.
+ */
+void __init xen_add_remap_nonram(phys_addr_t maddr, phys_addr_t paddr,
+				 unsigned long size)
+{
+	if (nr_nonram_remap == NR_NONRAM_REMAP) {
+		xen_raw_console_write("Number of required E820 entry remapping actions exceed maximum value\n");
+		BUG();
+	}
+
+	xen_nonram_remap[nr_nonram_remap].maddr = maddr;
+	xen_nonram_remap[nr_nonram_remap].paddr = paddr;
+	xen_nonram_remap[nr_nonram_remap].size = size;
+
+	nr_nonram_remap++;
+}
+
 #ifdef CONFIG_XEN_DEBUG_FS
 #include <linux/debugfs.h>
 static int p2m_dump_show(struct seq_file *m, void *v)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 9a27d1d653d3..e1b782e823e6 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -47,6 +47,9 @@ void xen_mm_unpin_all(void);
 #ifdef CONFIG_X86_64
 void __init xen_relocate_p2m(void);
 #endif
+void __init xen_do_remap_nonram(void);
+void __init xen_add_remap_nonram(phys_addr_t maddr, phys_addr_t paddr,
+				 unsigned long size);
 
 void __init xen_chk_is_e820_usable(phys_addr_t start, phys_addr_t size,
 				   const char *component);
-- 
2.43.0