Re: [PATCH v2 1/1] x86/fred: Fix system hang during S4 resume with FRED enabled

[H. Peter Anvin]

On April 1, 2025 12:57:27 AM PDT, "Xin Li (Intel)" <xin@xxxxxxxxx> wrote:
>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@xxxxxxxxx>
>Reported-by: Todd Brandt <todd.e.brandt@xxxxxxxxx>
>Suggested-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
>Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
>Tested-by: Todd Brandt <todd.e.brandt@xxxxxxxxx>
>Cc: Andy Lutomirski <luto@xxxxxxxxxx>
>Cc: Brian Gerst <brgerst@xxxxxxxxx>
>Cc: Juergen Gross <jgross@xxxxxxxx>
>Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
>Cc: stable@xxxxxxxxxxxxxxx # 6.9+
>---
>
>Change in v2:
>* Rewrite the change log and in-code comments based on Rafael's feedback.
>---
> 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 63230ff8cf4f..08e76a5ca155 100644
>--- a/arch/x86/power/cpu.c
>+++ b/arch/x86/power/cpu.c
>@@ -27,6 +27,7 @@
> #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;
>@@ -231,6 +232,19 @@ 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
>
>base-commit: 535bd326c5657fe570f41b1f76941e449d9e2062

Reviewed-by: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>