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Fri, 19 Dec 2025 23:19:29 +0000 (UTC) Message-ID: Date: Fri, 19 Dec 2025 15:19:28 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/CPU/AMD: avoid printing reset reasons on Xen domU To: Sean Christopherson , Borislav Petkov Cc: linux-kernel@vger.kernel.org, mario.limonciello@amd.com, darwi@linutronix.de, sandipan.das@amd.com, kai.huang@intel.com, me@mixaill.net, yazen.ghannam@amd.com, riel@surriel.com, peterz@infradead.org, hpa@zytor.com, x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, xen-devel@lists.xenproject.org, stable@vger.kernel.org References: <20251219010131.12659-1-ariadne@ariadne.space> <7C6C14C2-ABF8-4A94-B110-7FFBE9D2ED79@alien8.de> Content-Language: en-US From: Ariadne Conill In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Authority-Info: v=2.4 cv=Fas6BZ+6 c=1 sm=1 tr=0 ts=6945dd90 cx=c_apl:c_pps a=bsP7O+dXZ5uKcj+dsLqiMw==:117 a=bsP7O+dXZ5uKcj+dsLqiMw==:17 a=IkcTkHD0fZMA:10 a=MKtGQD3n3ToA:10 a=1oJP67jkp3AA:10 a=wP3pNCr1ah4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=kmYkUENqAAAA:8 a=cWRNjhkoAAAA:8 a=VwQbUJbxAAAA:8 a=jQPEHyspVSHZgeuGXSQA:9 a=QEXdDO2ut3YA:10 a=p9kz6gysRiz6SGr9lVkz:22 a=sVa6W5Aao32NNC1mekxh:22 X-Proofpoint-ORIG-GUID: PrgxWHdnMqmT56j-36miK5PuOTkgt8vm X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMjE5MDE5NiBTYWx0ZWRfX1hQobANrkcwi fAOYdQ6SalVAYZ50ZyICd6lmGxyNCstXgvN2h7qvEzqWepamC0HYV1qNjmQl/noKu06j9ynh5PB X6I8nwhJKKoUnE78HqPDq2tdd+5nEdhDQuZFOrg6vOZH5N7bW6pSlMN9qflPI73b8z0a86ftDyP NsTuzn14/2gDFY253bCFbEk0DNTqKgqJiwOeMN3xh1Z2CFdiAfMIHq1atBGHHl0o5NmdH+oz/MS mK0bYKQfff0zG3/0IRmZUdziAXbHX1CM5qcZVF7epZISJod1ri5IihY/OPirX1oGmM6ZmfoD3UL 0HsaPtA01XwwRL9+yGf X-Proofpoint-GUID: PrgxWHdnMqmT56j-36miK5PuOTkgt8vm X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-19_08,2025-12-19_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 clxscore=1030 mlxlogscore=999 bulkscore=0 malwarescore=0 mlxscore=0 spamscore=0 phishscore=0 adultscore=0 suspectscore=0 classifier=spam authscore=0 adjust=0 reason=mlx scancount=1 engine=8.22.0-2510240001 definitions=main-2512190196 X-JNJ: AAAAAAABCeDZeZABUl1JBQZUFV5IHr6VVYAh9hTgMK6DZMe7v9k9M5CZQCnXlaMiG2N5UpfcrLgKZJJrQoSKX2mJqV1pPPecVXEiW+S0H4n+gHaK0zTzj6Winp6wvqXLScyHgtvQ1K7MzL+Gktqfc7PBGbCsHKCSK6GLnqX9aTleGPFku21OKp49OQGlMVZlTFGFnPnVIhRibRG5zVWPUbV38vqZD1b12pzR9D1mvk6wNFDR8yZF1JcjSORncY5j0k8LDwSS5SviG59MsRhSSAjvhR03IiFPfevkdzoRyDde3geX8m8UV0KXP3EndWv9BFLPkj6D0ht4H+fXq2SaFf6KFEOG7GtK2+yYHBEnc1UBz2ZotTFfFLNQW/E8Cme0DshfAT0xIVHEWWTFjobZvtL8psRlam0SDNi6oktfi7nGCoD6u+ybqdUWDTF0ob1eSQDsIAiDXZqAIHH7ed1ZkcKhxDYWc18t0IcAwMpPOAOks+0X6fHn/Yc52HluCLS4Mr0MHAMsOh1REPSkahqeePtML95elCEZKpG5QGCshkrpLjnDwWrbq1I0pnr523aKP7fDsEZ5ldO1dKwSWJwFsjUuu8NlXPzRT8irDivscY7FVY26tiM/ntPHJJwBijs7JF8V3bXdP9DR6BoX4dGRte5qPzqYY7W2ij1UmblqIYpoEwhoYYBrHOv/BT29g61raMcLMlRQOXj6Rb4sAVEXoP9dFiEwnfBvx3Wt1TH3k2Pb3f0tjSl8eO9jxaCsidx++26dX98H7097CpjwjDdkvSrOpSKa23zAKTLBR8OnL5k14kVmLNYe9fCVe0bhO3ExpBAyad20d1veTQk3NebdxBuYEKkYqXndk55NkEZluk4f7u5HOtr80eDwmU/k08ZQLTw= Hi, On 12/19/25 08:09, Sean Christopherson wrote: > On Fri, Dec 19, 2025, Borislav Petkov wrote: >> On December 19, 2025 1:01:31 AM UTC, Ariadne Conill wrote: >>> Xen domU cannot access the given MMIO address for security reasons, >>> resulting in a failed hypercall in ioremap() due to permissions. > Why does that matter though? Ah, because set_pte() assumes success, and so > presumably the failed hypercall goes unnoticed and trying to access the MMIO > #PFs due to !PRESENT mapping. Yes, which results in the guest panicing on Zen platforms. >>> Fixes: ab8131028710 ("x86/CPU/AMD: Print the reason for the last reset") >>> Signed-off-by: Ariadne Conill >>> 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 >>> #endif >>> >>> +#include >>> + >>> #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 */ > Heh, Xen on Zen crime. > >>> + 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. > LOL, Ariadne, be honest, how much did Boris pay you? :-D Nothing :) At Edera we have been running with this patch for a few months, I just forgot to upstream it. I was reminded of this patch when an Alpine user opened a bug[0] demonstrating the same behavior on 6.18. [0]: https://gitlab.alpinelinux.org/alpine/aports/-/issues/17789 > Jokes aside, I suppose I'm fine adding a HYPERVISOR check, but at the same time, > how is this not a Xen bug? Refusing to create a mapping because the VM doesn't > have a device defined at a given GPA is pretty hostile behavior for a hypervisor. I think it would be better to fix this in a more generic way if we can. Ariadne