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 [tip: x86/urgent] x86/fred: Fix system hang during S4 resume with FRED enabled
 The following commit has been merged into the x86/urgent branch of tip:
-Commit-ID:     e5f1e8af9c9e151ecd665f6d2e36fb25fec3b110
+Commit-ID:     b578bfe07ae943937a2945a9f6ac4b497f4d4e09
-Gitweb:        https://git.kernel.org/tip/e5f1e8af9c9e151ecd665f6d2e36fb25fec3b110
+Gitweb:        https://git.kernel.org/tip/b578bfe07ae943937a2945a9f6ac4b497f4d4e09
 Author:        Xin Li (Intel) <xin@zytor.com>
-AuthorDate:    Tue, 01 Apr 2025 00:57:27 -07:00
+AuthorDate:    Tue, 25 Mar 2025 23:25:40 -07:00
 Committer:     Ingo Molnar <mingo@kernel.org>
-CommitterDate: Tue, 01 Apr 2025 22:29:02 +02:00
+CommitterDate: Mon, 31 Mar 2025 14:19:35 +02:00
 x86/fred: Fix system hang during S4 resume with FRED enabled
-Upon a wakeup from S4, the restore kernel starts and initializes the
+During an S4 resume, the system first performs a cold power-on.  The
-FRED MSRs as needed from its perspective.  It then loads a hibernation
+kernel image is initially loaded to a random linear address, and the
-image, including the image kernel, and attempts to load image pages
+FRED MSRs are initialized.  Subsequently, the S4 image is loaded,
-directly into their original page frames used before hibernation unless
+and the kernel image is relocated to its original address from before
-those frames are currently in use.  Once all pages are moved to their
+the S4 suspend.  Due to changes in the kernel text and data mappings,
-original locations, it jumps to a "trampoline" page in the image kernel.
+the FRED MSRs must be reinitialized with new values.
-At this point, the image kernel takes control, but the FRED MSRs still
+[ mingo: Rephrased & clarified the comments. ]
 contain values set by the restore kernel, which may differ from those
 set by the image kernel before hibernation.  Therefore, the image kernel
 must ensure the FRED MSRs have the same values as before hibernation.
 Since these values depend only on the location of the kernel text and
 data, they can be recomputed from scratch.
 Reported-by: Xi Pardee <xi.pardee@intel.com>
 Reported-by: Todd Brandt <todd.e.brandt@intel.com>
-Tested-by: Todd Brandt <todd.e.brandt@intel.com>
 Suggested-by: H. Peter Anvin (Intel) <hpa@zytor.com>
 Signed-off-by: Xin Li (Intel) <xin@zytor.com>
 Signed-off-by: Ingo Molnar <mingo@kernel.org>
-Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
+Tested-by: Todd Brandt <todd.e.brandt@intel.com>
 Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
 Cc: Andy Lutomirski <luto@kernel.org>
 Cc: Brian Gerst <brgerst@gmail.com>
 Cc: Juergen Gross <jgross@suse.com>
 Cc: Linus Torvalds <torvalds@linux-foundation.org>
-Link: https://lore.kernel.org/r/20250401075728.3626147-1-xin@zytor.com
+Link: https://lore.kernel.org/r/20250326062540.820556-1-xin@zytor.com
 ---
- arch/x86/power/cpu.c | 14 ++++++++++++++
+ arch/x86/power/cpu.c | 20 ++++++++++++++++++++
-file changed, 14 insertions(+)
+file changed, 20 insertions(+)
 diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
 index XXXXXXX..XXXXXXX 100644
 --- a/arch/x86/power/cpu.c
 +++ b/arch/x86/power/cpu.c
 ...
       */
  #ifdef CONFIG_X86_64
      wrmsrl(MSR_GS_BASE, ctxt->kernelmode_gs_base);
 +
 +    /*
-+     * Reinitialize FRED to ensure the FRED MSRs contain the same values
++     * Restore FRED settings.
 +     * as before hibernation.
 +     *
-+     * Note, the setup of FRED RSPs requires access to percpu data
++     * FRED settings can be completely derived from
-+     * structures.  Therefore, FRED reinitialization can only occur after
++     * current kernel text and data data mappings, thus
-+     * the percpu access pointer (i.e., MSR_GS_BASE) is restored.
++     * nothing needs to be saved and restored.
 +     *
 +     * As such, simply re-initialize FRED to restore the FRED
 +     * settings. Note that any changes to text and data mappings
 +     * after S4 resume will generate different FRED configuration
 +     * values.
 +     *
 +     * Also, FRED RSPs setup needs to access per-CPU data structures.
 +     */
 +    if (ctxt->cr4 & X86_CR4_FRED) {
 +        cpu_init_fred_exceptions();
 +        cpu_init_fred_rsps();
 +    }
  #else
      loadsegment(fs, __KERNEL_PERCPU);
  #endif

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

Commit-ID:     e5f1e8af9c9e151ecd665f6d2e36fb25fec3b110
Gitweb:        https://git.kernel.org/tip/e5f1e8af9c9e151ecd665f6d2e36fb25fec3b110
Author:        Xin Li (Intel) <xin@zytor.com>
AuthorDate:    Tue, 01 Apr 2025 00:57:27 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Tue, 01 Apr 2025 22:29:02 +02:00

x86/fred: Fix system hang during S4 resume with FRED enabled

Upon a wakeup from S4, the restore kernel starts and initializes the
FRED MSRs as needed from its perspective.  It then loads a hibernation
image, including the image kernel, and attempts to load image pages
directly into their original page frames used before hibernation unless
those frames are currently in use.  Once all pages are moved to their
original locations, it jumps to a "trampoline" page in the image kernel.

At this point, the image kernel takes control, but the FRED MSRs still
contain values set by the restore kernel, which may differ from those
set by the image kernel before hibernation.  Therefore, the image kernel
must ensure the FRED MSRs have the same values as before hibernation.
Since these values depend only on the location of the kernel text and
data, they can be recomputed from scratch.

Reported-by: Xi Pardee <xi.pardee@intel.com>
Reported-by: Todd Brandt <todd.e.brandt@intel.com>
Tested-by: Todd Brandt <todd.e.brandt@intel.com>
Suggested-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250401075728.3626147-1-xin@zytor.com
---
 arch/x86/power/cpu.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index XXXXXXX..XXXXXXX 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -XXX,XX +XXX,XX @@
 #include <asm/mmu_context.h>
 #include <asm/cpu_device_id.h>
 #include <asm/microcode.h>
+#include <asm/fred.h>
 
 #ifdef CONFIG_X86_32
 __visible unsigned long saved_context_ebx;
@@ -XXX,XX +XXX,XX @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
 	 */
 #ifdef CONFIG_X86_64
 	wrmsrl(MSR_GS_BASE, ctxt->kernelmode_gs_base);
+
+	/*
+	 * Reinitialize FRED to ensure the FRED MSRs contain the same values
+	 * as before hibernation.
+	 *
+	 * Note, the setup of FRED RSPs requires access to percpu data
+	 * structures.  Therefore, FRED reinitialization can only occur after
+	 * the percpu access pointer (i.e., MSR_GS_BASE) is restored.
+	 */
+	if (ctxt->cr4 & X86_CR4_FRED) {
+		cpu_init_fred_exceptions();
+		cpu_init_fred_rsps();
+	}
 #else
 	loadsegment(fs, __KERNEL_PERCPU);
 #endif

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

Commit-ID:     b578bfe07ae943937a2945a9f6ac4b497f4d4e09
Gitweb:        https://git.kernel.org/tip/b578bfe07ae943937a2945a9f6ac4b497f4d4e09
Author:        Xin Li (Intel) <xin@zytor.com>
AuthorDate:    Tue, 25 Mar 2025 23:25:40 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 31 Mar 2025 14:19:35 +02:00

x86/fred: Fix system hang during S4 resume with FRED enabled

During an S4 resume, the system first performs a cold power-on.  The
kernel image is initially loaded to a random linear address, and the
FRED MSRs are initialized.  Subsequently, the S4 image is loaded,
and the kernel image is relocated to its original address from before
the S4 suspend.  Due to changes in the kernel text and data mappings,
the FRED MSRs must be reinitialized with new values.

[ mingo: Rephrased & clarified the comments. ]

Reported-by: Xi Pardee <xi.pardee@intel.com>
Reported-by: Todd Brandt <todd.e.brandt@intel.com>
Suggested-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Todd Brandt <todd.e.brandt@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250326062540.820556-1-xin@zytor.com
---
 arch/x86/power/cpu.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index XXXXXXX..XXXXXXX 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -XXX,XX +XXX,XX @@
 #include <asm/mmu_context.h>
 #include <asm/cpu_device_id.h>
 #include <asm/microcode.h>
+#include <asm/fred.h>
 
 #ifdef CONFIG_X86_32
 __visible unsigned long saved_context_ebx;
@@ -XXX,XX +XXX,XX @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
 	 */
 #ifdef CONFIG_X86_64
 	wrmsrl(MSR_GS_BASE, ctxt->kernelmode_gs_base);
+
+	/*
+	 * Restore FRED settings.
+	 *
+	 * FRED settings can be completely derived from
+	 * current kernel text and data data mappings, thus
+	 * nothing needs to be saved and restored.
+	 *
+	 * As such, simply re-initialize FRED to restore the FRED
+	 * settings. Note that any changes to text and data mappings
+	 * after S4 resume will generate different FRED configuration
+	 * values.
+	 *
+	 * Also, FRED RSPs setup needs to access per-CPU data structures.
+	 */
+	if (ctxt->cr4 & X86_CR4_FRED) {
+		cpu_init_fred_exceptions();
+		cpu_init_fred_rsps();
+	}
 #else
 	loadsegment(fs, __KERNEL_PERCPU);
 #endif