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Sun, 21 Jul 2024 23:59:45 -0700 (PDT) Message-ID: Date: Mon, 22 Jul 2024 08:59:44 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 6/8] xen/riscv: introduce generic Xen page table handling To: Julien Grall Cc: Andrew Cooper , Stefano Stabellini , Bertrand Marquis , Michal Orzel , Volodymyr Babchuk , Oleksii Kurochko , xen-devel@lists.xenproject.org References: <5187f606-0a1c-4812-8f8c-13301f0aba8c@xen.org> 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: <5187f606-0a1c-4812-8f8c-13301f0aba8c@xen.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 21.07.2024 11:02, Julien Grall wrote: > Hi, > > On 12/07/2024 17:22, Oleksii Kurochko wrote: >> At least, between Arm and RISC-V most of the code related to Xen page >> table handling are common. >> >> This GENERIC_PT code is based on Arm's arm/mmu/pt.c except some minor >> changes such as introduction of the following functions: >> * get_root_page() >> * xen_pt_check_contig() >> * set_pte_table_bit() >> * sanity_arch_specific_pte_checks() >> * get_contig_bit() >> * set_pte_permissions() >> * flush_xen_tlb_range_va() >> It was done because not every functions has the generic pte_flags and >> it could be a different positions of the PTE bits in a PTE. > While I am always in favor of trying to avoid code duplication, I am not > sure the page-tables are one that should be. > > For instance, you don't have the concept of contiguous page in RISC-V (I > see you introduce dummy flags, but IMHO this is a bit of a hack). All > the code was also written in a way to avoid temporary conflict mappings. > This is to avoid using Break-Before-Make. But on newer hardware this > could be relaxed. > > I am interested to know what the others thinks. I share the concern; I was rather surprised to see the title, but - not having had the time to look at the patch yet - was kind of guessing (hoping) it wasn't really what the title said. Page table handling quite likely wants to remain arch-specific. Jan