From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f41.google.com (mail-wm1-f41.google.com [209.85.128.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DAB2B36C584 for ; Tue, 24 Feb 2026 09:39:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771925947; cv=none; b=DOqbP3UIuW8C1Cyd1EQxr5Ej3lHzh/BLNfqIC/YKor7JWsAnY1XetMzjj/2sXtrXEMys0j6bkuVJrgszGrNQ9A4aHgpmjKpXzkMETzN1M0/oymObc6hza3rxgqhN3GoUrCJXOm+fyK2/ACFFXtboPY2TLmsd03I6c82DQj6h/kw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771925947; c=relaxed/simple; bh=ZWYy7UrmABDxNQ6m5/atO/se4HvcKhmT5XKO01vqGTE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=s4SZDlfHmpZIuzNXyc8vxC8cuPOCGwpbEsWsqZAg7/cHWXEQAt7gimsWKzmvp+my9+uciAvbmAnr2643TwcdAeTI3j1XrtptHUUP19jXHnaH7cs7SsZx4mviwtUvdxgmHDRrv26XK+btyGu4dDvh+9qWJcW16jQwGqWOoT5Zgs0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=cRqJRuO6; arc=none smtp.client-ip=209.85.128.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="cRqJRuO6" Received: by mail-wm1-f41.google.com with SMTP id 5b1f17b1804b1-48379a42f76so40791275e9.0 for ; Tue, 24 Feb 2026 01:39:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1771925944; x=1772530744; darn=vger.kernel.org; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to; bh=oPdr4BEdKwpgwMsKfhbkN2p3SMdJv/s6l0UrV3280b0=; b=cRqJRuO6W5viykdpFv48B45y3bRVmKaArZYSKFpSusttZwE0pHkWZv+PLbAYGk6vHv LBvksj0ow/uHFhLVqFkZwXPvCPCz6AqKAHQ1n3e+7Wwc0iy2Hot0YZMTKZwCdsoZXbyQ hQOTIR20DFNcXt8MJWgpMkgwOt1DD+LdgWptipJpxW6LliAHfwMhX9qWd00CbqfiZskY UvuoeEym3lS/OKcC0sWQLAIfSH2qmVIvZ8Z/wb5834UFkKvW5axG/fUhvcFW2hdq2j3r 2TugLaKWNBlj1eXxwDlF8jULsQLO4jp6tvqBLf7Ypfr/md5L00D2fmvI2ZLxrlIQ1o5+ 1+rw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771925944; x=1772530744; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=oPdr4BEdKwpgwMsKfhbkN2p3SMdJv/s6l0UrV3280b0=; b=fEkMSM5bS9/WSiuAqqJEHtJM1D4Rgew9ZKuLECtVaIhl2ICBq/7Ua4wfWTafjETAe9 1nFX3HsWcaNJcW1o01dQ+Ha3k3vTZJtOB6quGe23tnW2VlalBEKI+o4osBjzrhm1h3BH clpZP7AIlldA2NcrF9xjMfhzw/TfXY0d3bKCvKp4UV46g4vRzRzDbiRtPNPXVTKhflcy hceH0YydQFhm+o3do45nOkEXKCI2BZ5rv2goMwI02qFa82dOooK7BGij8oda0ATTxM6C tSufL27A5DDrdluouQtXXndX9imVbhP4OhRfvDVJAHFdhjzrTOpJAFcT/4n3FbHiadBK 2lmQ== X-Forwarded-Encrypted: i=1; AJvYcCURhSmjmyz+9NNDGzHxun9TNH9vQfBpsviRemVd0MlEUUGA0nTC6vX/Pmox1pA3TaISkvoo7F7sE/A0V68=@vger.kernel.org X-Gm-Message-State: AOJu0YylSe5Y+vHuJssjningKZgOYETwdZ30I1vqxpTng8ewZTGePVaB 7qqMPeCedE68xwSMrh/xbl06an/6kahf913LpodWdmLeCnEyoojfdcbxV+46P3YLRQ== X-Gm-Gg: AZuq6aIXJqY9lGr0yEmZiIemslNAT1t0WI22nxOlkvR31fSYrABzVBB3LvX9C/JoU9W 7p6M7L6uBRwfv5npJtrNUkpsTzPRnbtyrDCdXgOUbipvK7B4pAaUuSwdIvJyM/nBdFSU6urV5ha WpK7VpeHg2RicR0VfkTHywTQUKunBDnHKE9/sBS+mr4hoQR7PKmK/uElWiLUisJnGLHL/UwKwVV UAbPNGIBU3MHsKle7r0VXFabLLjxViRxCeyS5eN08JfEjHKgNrs/b6wwXK7sNTC7IUjzdKndSXy QzcMkTfJ4wbejNR+aNnHvKMKAh7H8UGWJ7/9nVgEAi10NzdwGh8Osl+fgW436z5zd0fQPfp8EiG MhZ8hg7ZiIqMIN2+IEmacY3LZ5BQbybxnXaiAzvMcCmL1js0hY+UJb+20wryvHWGta8Ber2A1Oi 9aRkadYTjmtn0jJN+YuDkbeRKF/DSowYZ/dM8/MqgCAA/ROBKaKNZos+K0Q7T7DsujqEYxGpwPM lhOHIOqwaUkcXY= X-Received: by 2002:a05:600c:3484:b0:459:db7b:988e with SMTP id 5b1f17b1804b1-483a9603734mr192449605e9.13.1771925944253; Tue, 24 Feb 2026 01:39:04 -0800 (PST) Received: from [10.156.60.236] (ip-037-024-206-209.um08.pools.vodafone-ip.de. [37.24.206.209]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43970c09897sm25926203f8f.17.2026.02.24.01.39.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Feb 2026 01:39:03 -0800 (PST) Message-ID: Date: Tue, 24 Feb 2026 10:39:03 +0100 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 v2] xen/acpi-processor: fix _CST detection using undersized evaluation buffer To: David Thomson , jgross@suse.com Cc: boris.ostrovsky@oracle.com, olekstysh@gmail.com, tglx@linutronix.de, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org References: <20260224093707.19679-1-dt@linux-mail.net> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <20260224093707.19679-1-dt@linux-mail.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 24.02.2026 10:37, David Thomson wrote: > read_acpi_id() attempts to evaluate _CST using a stack buffer of > sizeof(union acpi_object) (48 bytes), but _CST returns a nested Package > of sub-Packages (one per C-state, each containing a register descriptor, > type, latency, and power) requiring hundreds of bytes. The evaluation > always fails with AE_BUFFER_OVERFLOW. > > On modern systems using FFH/MWAIT entry (where pblk is zero), this > causes the function to return before setting the acpi_id_cst_present > bit. In check_acpi_ids(), flags.power is then zero for all Phase 2 CPUs > (physical CPUs beyond dom0's vCPU count), so push_cxx_to_hypervisor() is > never called for them. > > On a system with dom0_max_vcpus=2 and 8 physical CPUs, only PCPUs 0-1 > receive C-state data. PCPUs 2-7 are stuck in C0/C1 idle, unable to > enter C2/C3. This costs measurable wall power (4W observed on an Intel > Core Ultra 7 265K with Xen 4.20). > > The function never uses the _CST return value -- it only needs to know > whether _CST exists. Replace the broken acpi_evaluate_object() call with > acpi_has_method(), which correctly detects _CST presence using > acpi_get_handle() without any buffer allocation. This brings C-state > detection to parity with the P-state path, which already works correctly > for Phase 2 CPUs. > > Fixes: 59a568029181 ("xen/acpi-processor: C and P-state driver that uploads said data to hypervisor.") > Signed-off-by: David Thomson Reviewed-by: Jan Beulich