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Mon, 11 May 2026 03:41:03 -0700 (PDT) Message-ID: Date: Mon, 11 May 2026 12:41:05 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 9/9] x86/mwait-idle: Add C-states validation To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper References: <7b7a677e-a5b9-42c8-beec-3c506b4eac52@suse.com> <57233a5d-3944-433c-a7c5-a1a491a2c1dd@suse.com> 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: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-purgate-ID: tlsNG-c1860d/1778496064-C5784DB1-064AD845/0/0 X-purgate-type: clean X-purgate-size: 2912 On 08.05.2026 09:38, Roger Pau Monné wrote: > On Mon, May 04, 2026 at 11:34:40AM +0200, Jan Beulich wrote: >> On 24.04.2026 21:15, Roger Pau Monné wrote: >>> On Thu, Mar 12, 2026 at 05:58:21PM +0100, Jan Beulich wrote: >>>> @@ -1589,6 +1594,41 @@ static char *__init get_cmdline_field(ch >>>> } >>>> >>>> /** >>>> + * validate_cmdline_cstate - Validate a C-state from cmdline. >>>> + * @state: The C-state to validate. >>>> + * @prev_state: The previous C-state in the table or NULL. >>>> + * >>>> + * Return: 0 if the C-state is valid or -EINVAL otherwise. >>> >>> Hm, I know we picked this up from upstream, but this function would >>> better return a boolean, rather than 0 or -EINVAL. >> >> I agree, but I didn't want to deviate from their code purely for cosmetic >> reasons. >> >>>> +static int __init validate_cmdline_cstate(struct cpuidle_state *state, >>>> + struct cpuidle_state *prev_state) >>>> +{ >>>> + if (state->exit_latency == 0) >>>> + /* Exit latency 0 can only be used for the POLL state */ >>>> + return -EINVAL; >>>> + >>>> + if (state->exit_latency > MAX_CMDLINE_LATENCY_US) >>>> + return -EINVAL; >>>> + >>>> + if (state->target_residency > MAX_CMDLINE_RESIDENCY_US) >>>> + return -EINVAL; >>>> + >>>> + if (state->target_residency < state->exit_latency) >>>> + return -EINVAL; >>>> + >>>> + if (!prev_state) >>>> + return 0; >>>> + >>>> + if (state->exit_latency <= prev_state->exit_latency) >>>> + return -EINVAL; >>>> + >>>> + if (state->target_residency <= prev_state->target_residency) >>>> + return -EINVAL; >>> >>> I'm not an expert on C-states, but isn't this checking against the >>> previous value kind of defeating part of the purpose of the command >>> line? >> >> I don't know. The question would need raising to the author. >> >>> Also, it might help to also write down those limits in the command >>> line documentation. >> >> What do you mean there? Some of the values are universal, but some >> checks are against model-specific values. I don't think you mean to >> enumerate them all? > > Maybe it's indeed not very useful. What I referring to was something > along the lines of: "the command line provided residency and latency > values must be smaller than the default ones". As noted above it > seems weird to me than higher than current values cannot be set, > albeit I have no idea what's the expected usage of this interface. Hmm, while meaning to make this change I came to wonder: What exactly do you refer to by "current values" and "default ones"? prev_state here isn't "previous state" as in "before this option was parsed", but as in "next lower C-state", as per prev_state = i ? &cmdline_states[i - 1] : NULL; ahead of the call site. Instead what I'm inclined to do (despite deviating from the original) is to constify the function's parameters. Jan