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Thu, 25 Jul 2024 02:26:33 -0700 (PDT) Message-ID: <7588feb4-dc42-4bf3-85db-7aaac201a2ff@suse.com> Date: Thu, 25 Jul 2024 11:26:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/3] x86/mm: add API for marking only part of a MMIO page read only To: =?UTF-8?Q?Marek_Marczykowski-G=C3=B3recki?= Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , xen-devel@lists.xenproject.org References: <4bea5034cda37f35cd04115bebcccb52e3ea719e.1721704980.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: <4bea5034cda37f35cd04115bebcccb52e3ea719e.1721704980.git-series.marmarek@invisiblethingslab.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 23.07.2024 05:24, Marek Marczykowski-Górecki wrote: > +static int __init subpage_mmio_ro_add_page( > + mfn_t mfn, > + unsigned int offset_s, > + unsigned int offset_e) > +{ > + struct subpage_ro_range *entry = NULL; > + bool new_entry = false; > + unsigned int i; > + > + entry = subpage_mmio_find_page(mfn); > + if ( !entry ) > + { > + entry = xzalloc(struct subpage_ro_range); > + if ( !entry ) > + return -ENOMEM; > + entry->mfn = mfn; > + list_add(&entry->list, &subpage_ro_ranges); > + new_entry = true; > + } > + > + for ( i = offset_s; i <= offset_e; i += MMIO_RO_SUBPAGE_GRAN ) > + { > + bool oldbit = __test_and_set_bit(i / MMIO_RO_SUBPAGE_GRAN, > + entry->ro_elems); > + ASSERT(!oldbit); > + } > + > + return new_entry ? 0 : 1; Imo simply !new_entry would be more concise. > +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; > + > + /* > + * In release, build unaligned start will protect larger area, I think the first comma wants to move past "build". > + * so tolerate it. > + * But unaligned size would result in smaller area, so deny it. > + */ > + ASSERT(IS_ALIGNED(start, MMIO_RO_SUBPAGE_GRAN)); > + ASSERT(IS_ALIGNED(size, MMIO_RO_SUBPAGE_GRAN)); > + if ( !IS_ALIGNED(size, MMIO_RO_SUBPAGE_GRAN) ) > + return -EINVAL; I hoped you would, when adding the comment, recall an earlier comment of mine: If you want to tolerate mis-aligned start in release builds, you need to make further adjustments to the subsequent logic (at which point the respective assertion may become pointless); see below. While things may work okay without (I didn't fully convince myself either way), the main point here is that you want to make sure we test in debug builds what's actually used in release one. Hence subtleties like this would better be dealt with uniformly between release and debug builds. > + 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; > + } > + else > + { > + subpage_start = PAGE_OFFSET(start); > + subpage_end = PAGE_OFFSET(end) != PAGE_SIZE - 1; > + } Neither of the two subpage_start calculations is correct when start is misaligned, but within the first 8 bytes of a page. Jan