linux-kernel - [PATCH 2/2] x86/xen: fix memblock

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Message-ID: <20240725073116.14626-3-roger.pau@citrix.com>
Date: Thu, 25 Jul 2024 09:31:15 +0200
From: Roger Pau Monne <roger.pau@...rix.com>
To: xen-devel@...ts.xenproject.org,
	linux-kernel@...r.kernel.org,
	Juergen Gross <jgross@...e.com>,
	Roger Pau Monne <roger.pau@...rix.com>
Cc: 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>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 2/2] x86/xen: fix memblock_reserve() usage on PVH

The current usage of memblock_reserve() in init_pvh_bootparams() is done before
the .bss is zeroed, and that used to be fine when
memblock_reserved_init_regions implicitly ended up in the .meminit.data
section.  However after commit 73db3abdca58c memblock_reserved_init_regions
ends up in the .bss section, thus breaking it's usage before the .bss is
cleared.

Move and rename the call to xen_reserve_extra_memory() so it's done in the
x86_init.oem.arch_setup hook, which gets executed after the .bss has been
zeroed, but before calling e820__memory_setup().

Fixes: 38620fc4e893 ('x86/xen: attempt to inflate the memory balloon on PVH')
Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
---
While the commit that introduced the user-noticeable regression is
73db3abdca58c, I think 38620fc4e893 should have been more careful to not
initialize the memblock ranges ahead of the .bss zeroing.
---
 arch/x86/include/asm/xen/hypervisor.h |  5 -----
 arch/x86/platform/pvh/enlighten.c     |  3 ---
 arch/x86/xen/enlighten_pvh.c          | 15 ++++++++++++---
 3 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/arch/x86/include/asm/xen/hypervisor.h b/arch/x86/include/asm/xen/hypervisor.h
index 64fbd2dbc5b7..a9088250770f 100644
--- a/arch/x86/include/asm/xen/hypervisor.h
+++ b/arch/x86/include/asm/xen/hypervisor.h
@@ -62,11 +62,6 @@ void xen_arch_unregister_cpu(int num);
 #ifdef CONFIG_PVH
 void __init xen_pvh_init(struct boot_params *boot_params);
 void __init mem_map_via_hcall(struct boot_params *boot_params_p);
-#ifdef CONFIG_XEN_PVH
-void __init xen_reserve_extra_memory(struct boot_params *bootp);
-#else
-static inline void xen_reserve_extra_memory(struct boot_params *bootp) { }
-#endif
 #endif
 
 /* Lazy mode for batching updates / context switch */
diff --git a/arch/x86/platform/pvh/enlighten.c b/arch/x86/platform/pvh/enlighten.c
index 8c2d4b8de25d..944e0290f2c0 100644
--- a/arch/x86/platform/pvh/enlighten.c
+++ b/arch/x86/platform/pvh/enlighten.c
@@ -75,9 +75,6 @@ static void __init init_pvh_bootparams(bool xen_guest)
 	} else
 		xen_raw_printk("Warning: Can fit ISA range into e820\n");
 
-	if (xen_guest)
-		xen_reserve_extra_memory(&pvh_bootparams);
-
 	pvh_bootparams.hdr.cmd_line_ptr =
 		pvh_start_info.cmdline_paddr;
 
diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
index 91c6db4ec054..728a4366ca85 100644
--- a/arch/x86/xen/enlighten_pvh.c
+++ b/arch/x86/xen/enlighten_pvh.c
@@ -9,6 +9,7 @@
 #include <asm/io_apic.h>
 #include <asm/hypervisor.h>
 #include <asm/e820/api.h>
+#include <asm/setup.h>
 
 #include <xen/xen.h>
 #include <asm/xen/interface.h>
@@ -41,8 +42,9 @@ EXPORT_SYMBOL_GPL(xen_pvh);
  * hypervisor should notify us which memory ranges are suitable for creating
  * foreign mappings, but that's not yet implemented.
  */
-void __init xen_reserve_extra_memory(struct boot_params *bootp)
+static void __init pvh_reserve_extra_memory(void)
 {
+	struct boot_params *bootp = &boot_params;
 	unsigned int i, ram_pages = 0, extra_pages;
 
 	for (i = 0; i < bootp->e820_entries; i++) {
@@ -94,6 +96,14 @@ void __init xen_reserve_extra_memory(struct boot_params *bootp)
 	}
 }
 
+static void __init pvh_arch_setup(void)
+{
+	pvh_reserve_extra_memory();
+
+	if (xen_initial_domain())
+		xen_add_preferred_consoles();
+}
+
 void __init xen_pvh_init(struct boot_params *boot_params)
 {
 	u32 msr;
@@ -107,8 +117,7 @@ void __init xen_pvh_init(struct boot_params *boot_params)
 	pfn = __pa(hypercall_page);
 	wrmsr_safe(msr, (u32)pfn, (u32)(pfn >> 32));
 
-	if (xen_initial_domain())
-		x86_init.oem.arch_setup = xen_add_preferred_consoles;
+	x86_init.oem.arch_setup = pvh_arch_setup;
 	x86_init.oem.banner = xen_banner;
 
 	xen_efi_init(boot_params);
-- 
2.45.2