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Fri, 04 Apr 2025 03:00:44 -0700 (PDT) Message-ID: <93111e6d-976f-45b1-810c-c52c74efa215@suse.com> Date: Fri, 4 Apr 2025 12:00:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] xen/riscv: Increase XEN_VIRT_SIZE To: Oleksii Kurochko Cc: Alistair Francis , Bob Eshleman , Connor Davis , Andrew Cooper , Anthony PERARD , Michal Orzel , Julien Grall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Stefano Stabellini , xen-devel@lists.xenproject.org References: <54ebdcb7-071f-411f-803a-930dc330a497@suse.com> <32264ccb-e566-41e0-973f-5bc7d874f970@gmail.com> <9d7e1553-3af8-4fc3-a400-8714d9b68411@suse.com> <30d8e316-aff5-498a-b2bd-448e0b2518ae@gmail.com> <3c2127ec-63fb-457b-8229-fc8a2b9fbf00@suse.com> <14ac3e72-d21d-4b45-a434-d123152c0113@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 On 04.04.2025 10:43, Oleksii Kurochko wrote: > > On 4/4/25 9:52 AM, Jan Beulich wrote: >> On 04.04.2025 09:31, Oleksii Kurochko wrote: >>> On 4/4/25 8:56 AM, Jan Beulich wrote: >>>> On 03.04.2025 18:20, Oleksii Kurochko wrote: >>>>> On 4/1/25 6:04 PM, Jan Beulich wrote: >>>>>> On 01.04.2025 17:58, Oleksii Kurochko wrote: >>>>>>> On 3/31/25 6:14 PM, Jan Beulich wrote: >>>>>>>> On 31.03.2025 17:20, Oleksii Kurochko wrote: >>>>>>>>> + _AC(XEN_VIRT_START, UL) >> vpn1_shift; >>>>>>>>> + const unsigned long xen_virt_end_vpn = >>>>>>>>> + xen_virt_starn_vpn + ((XEN_VIRT_SIZE >> vpn1_shift) - 1); >>>>>>>>> + >>>>>>>>> if ((va >= DIRECTMAP_VIRT_START) && >>>>>>>>> (va <= DIRECTMAP_VIRT_END)) >>>>>>>>> return directmapoff_to_maddr(va - directmap_virt_start); >>>>>>>>> >>>>>>>>> - BUILD_BUG_ON(XEN_VIRT_SIZE != MB(2)); >>>>>>>>> - ASSERT((va >> (PAGETABLE_ORDER + PAGE_SHIFT)) == >>>>>>>>> - (_AC(XEN_VIRT_START, UL) >> (PAGETABLE_ORDER + PAGE_SHIFT))); >>>>>>>>> + BUILD_BUG_ON(XEN_VIRT_SIZE != MB(8)); >>>>>>>> Is it necessary to be != ? Won't > suffice? >>>>>>> It could be just > MB(2). Or perphaps >=. >>>>>>> = would make the build fail, wouldn't it? >>>>> I just realized that BUILD_BUG_ON() condition is compared to zero so actually everything what >>>>> will make the condition true will cause a build fail as inside it used !(condition). >>>> ??? >>> |BUILD_BUG_ON()| forces a compilation error if the given condition is true. Therefore, if the condition >>> |XEN_VIRT_SIZE != MB(2)| is changed to|XEN_VIRT_SIZE > MB(2)|, the condition will always evaluate to true >>> (assuming|XEN_VIRT_SIZE| is greater than 2 MB), which will result in a compilation error. >> Well, it was you who used MB(2) in a reply, when previously talk was of MB(8), >> and that to grow to MB(16). The BUILD_BUG_ON() is - aiui - about you having set >> aside enough page table space. Quite possibly the need for this BUILD_BUG_ON() >> then disappears altogether when XEN_VIRT_SIZE is properly taken into account >> for the number-of-page-tables calculation. In no event do I see why the MB(2) >> boundary would be relevant for anything going forward. > > Also, doesn’t|BUILD_BUG_ON()| affect how the|ASSERT()| that follows it is written? > > The changes, at the moment, look like: > + const unsigned int vpn1_shift = PAGETABLE_ORDER + PAGE_SHIFT; > + const unsigned long va_vpn = va >> vpn1_shift; > + const unsigned long xen_virt_start_vpn = > + _AC(XEN_VIRT_START, UL) >> vpn1_shift; > + const unsigned long xen_virt_end_vpn = > + xen_virt_start_vpn + ((XEN_VIRT_SIZE >> vpn1_shift) - 1); > + > if ((va >= DIRECTMAP_VIRT_START) && > (va <= DIRECTMAP_VIRT_END)) > return directmapoff_to_maddr(va - directmap_virt_start); > > - BUILD_BUG_ON(XEN_VIRT_SIZE != MB(2)); > - ASSERT((va >> (PAGETABLE_ORDER + PAGE_SHIFT)) == > - (_AC(XEN_VIRT_START, UL) >> (PAGETABLE_ORDER + PAGE_SHIFT))); > + BUILD_BUG_ON(XEN_VIRT_SIZE != MB(16)); > + ASSERT((va_vpn >= xen_virt_start_vpn) && (va_vpn <= xen_virt_end_vpn)); > > > If|XEN_VIRT_SIZE| is greater than|GB(1)|, then|xen_virt_end_vpn| may be calculated > incorrectly. > > For example, if|XEN_VIRT_START| is|0xFFFFFFFF80000000| and|XEN_VIRT_SIZE| is|0x40200000|, > then|(XEN_VIRT_SIZE >> vpn1_shift)| equals 513, whereas|va_vpn| is always in the range [0, 511], > but xen_virt_end_vpn will be greater then 511. > > So shouldn't it be checked before ASSERT() that XEN_VIRT_SIZE is <= GB(1): > BUILD_BUG_ON(XEN_VIRT_SIZE <= GB(1))? Yes, that would make sense. Jan