Xen doesn't offer MSR_FAM10H_MMIO_CONF_BASE to all guests.  This results
in the following warning:

  unchecked MSR access error: RDMSR from 0xc0010058 at rIP: 0xffffffff8101d19f (xen_do_read_msr+0x7f/0xa0)
  Call Trace:
   xen_read_msr+0x1e/0x30
   amd_get_mmconfig_range+0x2b/0x80
   quirk_amd_mmconfig_area+0x28/0x100
   pnp_fixup_device+0x39/0x50
   __pnp_add_device+0xf/0x150
   pnp_add_device+0x3d/0x100
   pnpacpi_add_device_handler+0x1f9/0x280
   acpi_ns_get_device_callback+0x104/0x1c0
   acpi_ns_walk_namespace+0x1d0/0x260
   acpi_get_devices+0x8a/0xb0
   pnpacpi_init+0x50/0x80
   do_one_initcall+0x46/0x2e0
   kernel_init_freeable+0x1da/0x2f0
   kernel_init+0x16/0x1b0
   ret_from_fork+0x30/0x50
   ret_from_fork_asm+0x1b/0x30

based on quirks for a "PNP0c01" device.  Treating MMCFG as disabled is the
right course of action, so no change is needed there.

This was most likely exposed by fixing the Xen MSR accessors to not be
silently-safe.

Fixes: 3fac3734c43a ("xen/pv: support selecting safe/unsafe msr accesses")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: Borislav Petkov <bp@alien8.de>
CC: Dave Hansen <dave.hansen@linux.intel.com>
CC: x86@kernel.org
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Yazen Ghannam <yazen.ghannam@amd.com>
CC: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
CC: Mario Limonciello <mario.limonciello@amd.com>
CC: Richard Gong <richard.gong@amd.com>
CC: Juergen Gross <jgross@suse.com>
CC: linux-kernel@vger.kernel.org

diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c
index 11fac09e3a8c..90e58b4e8237 100644
--- a/arch/x86/kernel/amd_nb.c
+++ b/arch/x86/kernel/amd_nb.c
@@ -143,7 +143,6 @@ bool __init early_is_amd_nb(u32 device)
 
 struct resource *amd_get_mmconfig_range(struct resource *res)
 {
-	u32 address;
 	u64 base, msr;
 	unsigned int segn_busn_bits;
 
@@ -151,13 +150,11 @@ struct resource *amd_get_mmconfig_range(struct resource *res)
 	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
 		return NULL;
 
-	/* assume all cpus from fam10h have mmconfig */
-	if (boot_cpu_data.x86 < 0x10)
+	/* Assume CPUs from fam10h have mmconfig, although not all VMs do */
+	if (boot_cpu_data.x86 < 0x10 ||
+	    rdmsrl_safe(MSR_FAM10H_MMIO_CONF_BASE, &msr))
 		return NULL;
 
-	address = MSR_FAM10H_MMIO_CONF_BASE;
-	rdmsrl(address, msr);
-
 	/* mmconfig is not enabled */
 	if (!(msr & FAM10H_MMIO_CONF_ENABLE))
 		return NULL;

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     14cb5d83068ecf15d2da6f7d0e9ea9edbcbc0457
Gitweb:        https://git.kernel.org/tip/14cb5d83068ecf15d2da6f7d0e9ea9edbcbc0457
Author:        Andrew Cooper <andrew.cooper3@citrix.com>
AuthorDate:    Fri, 07 Mar 2025 00:28:46 
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 07 Mar 2025 13:28:31 +01:00

x86/amd_nb: Use rdmsr_safe() in amd_get_mmconfig_range()

Xen doesn't offer MSR_FAM10H_MMIO_CONF_BASE to all guests.  This results
in the following warning:

  unchecked MSR access error: RDMSR from 0xc0010058 at rIP: 0xffffffff8101d19f (xen_do_read_msr+0x7f/0xa0)
  Call Trace:
   xen_read_msr+0x1e/0x30
   amd_get_mmconfig_range+0x2b/0x80
   quirk_amd_mmconfig_area+0x28/0x100
   pnp_fixup_device+0x39/0x50
   __pnp_add_device+0xf/0x150
   pnp_add_device+0x3d/0x100
   pnpacpi_add_device_handler+0x1f9/0x280
   acpi_ns_get_device_callback+0x104/0x1c0
   acpi_ns_walk_namespace+0x1d0/0x260
   acpi_get_devices+0x8a/0xb0
   pnpacpi_init+0x50/0x80
   do_one_initcall+0x46/0x2e0
   kernel_init_freeable+0x1da/0x2f0
   kernel_init+0x16/0x1b0
   ret_from_fork+0x30/0x50
   ret_from_fork_asm+0x1b/0x30

based on quirks for a "PNP0c01" device.  Treating MMCFG as disabled is the
right course of action, so no change is needed there.

This was most likely exposed by fixing the Xen MSR accessors to not be
silently-safe.

Fixes: 3fac3734c43a ("xen/pv: support selecting safe/unsafe msr accesses")
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250307002846.3026685-1-andrew.cooper3@citrix.com
---
 arch/x86/kernel/amd_nb.c |  9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/amd_nb.c b/arch/x86/kernel/amd_nb.c
index 11fac09..67e7737 100644
--- a/arch/x86/kernel/amd_nb.c
+++ b/arch/x86/kernel/amd_nb.c
@@ -143,7 +143,6 @@ bool __init early_is_amd_nb(u32 device)
 
 struct resource *amd_get_mmconfig_range(struct resource *res)
 {
-	u32 address;
 	u64 base, msr;
 	unsigned int segn_busn_bits;
 
@@ -151,13 +150,11 @@ struct resource *amd_get_mmconfig_range(struct resource *res)
 	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
 		return NULL;
 
-	/* assume all cpus from fam10h have mmconfig */
-	if (boot_cpu_data.x86 < 0x10)
+	/* Assume CPUs from Fam10h have mmconfig, although not all VMs do */
+	if (boot_cpu_data.x86 < 0x10 ||
+	    rdmsrl_safe(MSR_FAM10H_MMIO_CONF_BASE, &msr))
 		return NULL;
 
-	address = MSR_FAM10H_MMIO_CONF_BASE;
-	rdmsrl(address, msr);
-
 	/* mmconfig is not enabled */
 	if (!(msr & FAM10H_MMIO_CONF_ENABLE))
 		return NULL;