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Tue, 11 Jun 2024 04:26:22 -0700 (PDT) Message-ID: Date: Tue, 11 Jun 2024 13:26:21 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/2] x86/mm: add API for marking only part of a MMIO page read only To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: xen-devel@lists.xenproject.org, Andrew Cooper , =?UTF-8?Q?Marek_Marczykowski-G=C3=B3recki?= References: <30562c807ff2e434731a76d7110d48614a58884b.1716392340.git-series.marmarek@invisiblethingslab.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 11.06.2024 12:40, Roger Pau Monné wrote: > On Wed, May 22, 2024 at 05:39:03PM +0200, Marek Marczykowski-Górecki wrote: >> +int __init subpage_mmio_ro_add( >> + paddr_t start, >> + size_t size) >> +{ >> + mfn_t mfn_start = maddr_to_mfn(start); >> + paddr_t end = start + size - 1; >> + mfn_t mfn_end = maddr_to_mfn(end); >> + unsigned int offset_end = 0; >> + int rc; >> + bool subpage_start, subpage_end; >> + >> + ASSERT(IS_ALIGNED(start, MMIO_RO_SUBPAGE_GRAN)); >> + ASSERT(IS_ALIGNED(size, MMIO_RO_SUBPAGE_GRAN)); >> + if ( !IS_ALIGNED(size, MMIO_RO_SUBPAGE_GRAN) ) >> + size = ROUNDUP(size, MMIO_RO_SUBPAGE_GRAN); >> + >> + if ( !size ) >> + return 0; >> + >> + if ( mfn_eq(mfn_start, mfn_end) ) >> + { >> + /* Both starting and ending parts handled at once */ >> + subpage_start = PAGE_OFFSET(start) || PAGE_OFFSET(end) != PAGE_SIZE - 1; >> + subpage_end = false; > > Given the intended usage of this, don't we want to limit to only a > single page? So that PFN_DOWN(start + size) == PFN_DOWN/(start), as > that would simplify the logic here? > > Mostly asking because I think for the usage of XHCI the registers that > need to be marked RO are all inside the same page, and hence would > like to avoid introducing logic to handle multipage ranges if that's > not tested at all. > >> + } >> + else >> + { >> + subpage_start = PAGE_OFFSET(start); >> + subpage_end = PAGE_OFFSET(end) != PAGE_SIZE - 1; >> + } >> + >> + spin_lock(&subpage_ro_lock); > > Do you really need the lock if modifications can only happen during > init? Xen initialization is single threaded, so you can likely avoid > the lock during boot. I was wondering the same, but then concluded the locking here is for the sake of completenese, not because it's strictly needed. Jan