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Mon, 26 Oct 2026 02:32:17 -0700 (PDT) Message-ID: <4526ac23-ca7c-40e2-a9d6-9d366369d3bb@suse.com> Date: Mon, 26 Oct 2026 10:32:15 +0100 X-Archived-By: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 3/4] xen/riscv: panic if the device tree advertises neither Svade nor Svadu To: Baptiste Le Duc Cc: Andrew Cooper , Anthony PERARD , Michal Orzel , Julien Grall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Stefano Stabellini , Alistair Francis , Connor Davis , Oleksii Kurochko , Zheng Zhang , xen-devel@lists.xenproject.org References: <1792164706.8631fc262581453bbf619ec5b2062170.1a14557373c0008425@vates.tech> <1792164867.8631fc262581453bbf619ec5b2062170.1a14559ab900008425@vates.tech> 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: <1792164867.8631fc262581453bbf619ec5b2062170.1a14559ab900008425@vates.tech> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-purgate-ID: tlsNG-4011c0/1793007137-518C5CFC-CAA5D9BC/10/78276251493 X-purgate-type: spam X-purgate-size: 2737 X-Spam-Status: No, score=-12.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On 16.10.2026 17:34, Baptiste Le Duc wrote: > p2m_set_pte_flags() presets the A/D bits of G-stage PTEs only when > RISCV_ISA_EXT_svade is set, which is correct only if the device tree is. > > The privileged spec allows exactly two schemes for updating the PTE A and D > bits: hardware sets them on access and on write, or accessing a page whose > A and/or D bit is clear raises a page fault so that software can set them > (ratified as Svade). Every implementation uses one of them, but platforms > designed before Svade and Svadu were ratified, such as the HiFive Premier > P550, may advertise neither. Xen then cannot tell which scheme is in > effect, so rather than guess, panic in riscv_fill_hwcap() when the device > tree advertises neither Svade nor Svadu, so that the device tree gets > fixed. > > Add Svadu to the known ISA extensions so it can be told apart from Svade. > The comment above the enum asks for new extensions to go at the bottom to > avoid shuffling, a leftover from Linux where the IDs were macros with > explicit values. Nothing depends on the enum values, so have the comment > say that multi-letter extensions follow the order of riscv_isa_ext[]. > > Suggested-by: Jan Beulich Did I, really? Iirc I left open whether to go the panic() route or the alternative one. Based on Andrew's clarification as to pre-Svad{e,u} behavior, I think I further tried to indicate that synthesizing the correct extension may be preferable, to allow older systems' DTs to be used as-is. In any event ... > @@ -674,6 +675,22 @@ void __init riscv_fill_hwcap(void) > "Zihintpause unavailable: cpu_relax() gives the CPU no hint; " > "wire up this platform's pause equivalent in cpu_relax()\n"); > > + /* > + * The privileged spec allows exactly two schemes for updating the PTE A > + * and D bits: > + * 1) hardware sets them on access and on write; > + * 2) accessing a page whose A and/or D bit is clear raises a page fault, > + * so that software can set them (ratified as Svade). > + * > + * Every implementation uses one of them, but may predate the extensions > + * and advertise neither. The device tree is then ambiguous: Xen cannot > + * tell which scheme is in effect, so panic and have the device tree > + * fixed. > + */ > + if ( !riscv_isa_extension_available(NULL, RISCV_ISA_EXT_svade) && > + !riscv_isa_extension_available(NULL, RISCV_ISA_EXT_svadu) ) > + panic("Device tree advertises neither Svade nor Svadu, A/D bits update scheme unknown\n"); ... this message leaves the observer to figure out what to do about the situation. Jan