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Tue, 07 Oct 2025 06:14:44 -0700 (PDT) Message-ID: Date: Tue, 7 Oct 2025 15:14:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 17/18] xen/riscv: add support of page lookup by GFN 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: <5065d9f1552fd940cc19087d8e00a0fa3519e66c.1758145428.git.oleksii.kurochko@gmail.com> <854ff53f-5af0-43bf-83b0-8e1e1e0deefc@suse.com> <577daeb5-d43f-4172-9a3b-2062c01b8d45@gmail.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: <577daeb5-d43f-4172-9a3b-2062c01b8d45@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 30.09.2025 17:37, Oleksii Kurochko wrote: > On 9/22/25 10:46 PM, Jan Beulich wrote: >> On 17.09.2025 23:55, Oleksii Kurochko wrote: >>> + if ( rc != P2M_TABLE_NORMAL ) >>> + break; >>> + } >>> + >>> + entry = table[offsets[level]]; >>> + >>> + if ( pte_is_valid(entry) ) >>> + { >>> + if ( t ) >>> + *t = p2m_get_type(entry); >>> + >>> + mfn = pte_get_mfn(entry); >>> + /* >>> + * The entry may point to a superpage. Find the MFN associated >>> + * to the GFN. >>> + */ >>> + mfn = mfn_add(mfn, >>> + gfn_x(gfn) & (BIT(P2M_LEVEL_ORDER(level), UL) - 1)); >> May want to assert that the respective bits of "mfn" are actually clear >> before this calculation. > > ASSERT(!(mfn & (BIT(P2M_LEVEL_ORDER(level), UL) - 1))); > Do you mean something like that? Yes. > I am not 100% sure that there is really need for that as page-fault exception > is raised if the PA is insufficienlty aligned: > Any level of PTE may be a leaf PTE, so in addition to 4 KiB pages, Sv39 supports > 2 MiB megapages and 1 GiB gigapages, each of which must be virtually and > physically aligned to a boundary equal to its size. A page-fault exception is > raised if the physical address is insufficiently aligned. But that would be raised only when a page walk encounters such a PTE. You may be altering a PTE here which never was involved in a page walk, though. Jan