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Mon, 09 Feb 2026 08:56:37 -0800 (PST) Message-ID: <7e8669d4-d1b6-47c7-ad08-da14f14fb4a4@suse.com> Date: Mon, 9 Feb 2026 17:56:38 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 4/6] xen/console: use memcpy() in console_init_ring() To: dmukhin@xen.org Cc: andrew.cooper3@citrix.com, anthony.perard@vates.tech, julien@xen.org, michal.orzel@amd.com, roger.pau@citrix.com, sstabellini@kernel.org, dmukhin@ford.com, xen-devel@lists.xenproject.org References: <20260205013606.3384798-1-dmukhin@ford.com> <20260205013606.3384798-5-dmukhin@ford.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: <20260205013606.3384798-5-dmukhin@ford.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 05.02.2026 02:36, dmukhin@xen.org wrote: > @@ -479,11 +479,23 @@ void __init console_init_ring(void) > opt_conring_size = PAGE_SIZE << order; > > nrspin_lock_irqsave(&console_lock, flags); > - for ( i = conringc ; i != conringp; i++ ) > - ring[i & (opt_conring_size - 1)] = conring[i & (conring_size - 1)]; > + > + start = conringc & (conring_size - 1); > + size = min(conringp - conringc, conring_size); Is this correct when the ring size actually shrinks? In such a case you want to copy the tail of the ring if not all of the original contents fits in the new one. But ... > + chunk = min(size, conring_size - start); > + > + memcpy(&ring[0], &conring[start], chunk); ... you start at its head. > + if ( size > chunk ) > + memcpy(&ring[chunk], &conring[0], size - chunk); > + > + /* Data is moved to [0..size), re-position conring pointers. */ > + conringc = 0; > + conringp = size; Why this unrelated change, which the description also doesn't mention? Since this is in an __init function, there's no race with read_console_ring(), but a static analysis tool may still (validly) spot one. Yet then there's also conring_flush(), which doesn't look to be using any locking either. Have you excluded that this function can run in a racing manner? Jan