Re: [PATCH] x86/CPU/AMD: avoid printing reset reasons on Xen domU

Borislav Petkov
2025-12-19T03:57:27Z

On December 19, 2025 1:01:31 AM UTC, Ariadne Conill <ariadne@ariadne.space> wrote:
>Xen domU cannot access the given MMIO address for security reasons,
>resulting in a failed hypercall in ioremap() due to permissions.
>
>Fixes: ab8131028710 ("x86/CPU/AMD: Print the reason for the last reset")
>Signed-off-by: Ariadne Conill <ariadne@ariadne.space>
>Cc: xen-devel@lists.xenproject.org
>Cc: stable@vger.kernel.org
>---
> arch/x86/kernel/cpu/amd.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
>diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
>index a6f88ca1a6b4..99308fba4d7d 100644
>--- a/arch/x86/kernel/cpu/amd.c
>+++ b/arch/x86/kernel/cpu/amd.c
>@@ -29,6 +29,8 @@
> # include <asm/mmconfig.h>
> #endif
>
>+#include <xen/xen.h>
>+
> #include "cpu.h"
>
> u16 invlpgb_count_max __ro_after_init = 1;
>@@ -1333,6 +1335,10 @@ static __init int print_s5_reset_status_mmio(void)
> if (!cpu_feature_enabled(X86_FEATURE_ZEN))
> return 0;
>
>+ /* Xen PV domU cannot access hardware directly, so bail for domU case */
>+ if (cpu_feature_enabled(X86_FEATURE_XENPV) && !xen_initial_domain())
>+ return 0;
>+
> addr = ioremap(FCH_PM_BASE + FCH_PM_S5_RESET_STATUS, sizeof(value));
> if (!addr)
> return 0;

Sean, looka here. The other hypervisor wants other checks.

Time to whip out the X86_FEATURE_HYPERVISOR check.
--
Small device. Typos and formatting crap