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

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Message-ID: <7C6C14C2-ABF8-4A94-B110-7FFBE9D2ED79@alien8.de>
Date: Fri, 19 Dec 2025 03:56:33 +0000
From: Borislav Petkov <bp@...en8.de>
To: Ariadne Conill <ariadne@...adne.space>, linux-kernel@...r.kernel.org,
 seanjc@...gle.com
CC: mario.limonciello@....com, darwi@...utronix.de, sandipan.das@....com,
 kai.huang@...el.com, me@...aill.net, yazen.ghannam@....com, riel@...riel.com,
 peterz@...radead.org, hpa@...or.com, x86@...nel.org, tglx@...utronix.de,
 mingo@...hat.com, dave.hansen@...ux.intel.com,
 xen-devel@...ts.xenproject.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/CPU/AMD: avoid printing reset reasons on Xen domU

On December 19, 2025 1:01:31 AM UTC, Ariadne Conill <ariadne@...adne.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@...adne.space>
>Cc: xen-devel@...ts.xenproject.org
>Cc: stable@...r.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