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Thu, 14 Aug 2025 03:45:42 -0700 (PDT) Message-ID: <3fbdd1fc-e739-42cf-892b-a561910a5693@suse.com> Date: Thu, 14 Aug 2025 12:45:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] pdx: cast PAGE_SIZE value ahead of shifting To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: Andrew Cooper , Anthony PERARD , Michal Orzel , Julien Grall , Stefano Stabellini , xen-devel@lists.xenproject.org References: <20250813125538.78174-1-roger.pau@citrix.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 14.08.2025 12:28, Roger Pau Monné wrote: > On Thu, Aug 14, 2025 at 09:18:45AM +0200, Jan Beulich wrote: >> On 13.08.2025 14:55, Roger Pau Monne wrote: >>> --- a/xen/common/pdx.c >>> +++ b/xen/common/pdx.c >>> @@ -288,7 +288,7 @@ bool __init pfn_pdx_compression_setup(paddr_t base) >>> >>> pfn_pdx_hole_shift = hole_shift; >>> pfn_pdx_bottom_mask = (1UL << bottom_shift) - 1; >>> - ma_va_bottom_mask = (PAGE_SIZE << bottom_shift) - 1; >>> + ma_va_bottom_mask = ((paddr_t)PAGE_SIZE << bottom_shift) - 1; >> >> Given >> >> #define PAGE_SIZE (_AC(1,L) << PAGE_SHIFT) >> >> this shouldn't be needed, except maybe for Arm32. There, however, ... >> >>> pfn_hole_mask = ((1UL << hole_shift) - 1) << bottom_shift; >> >> ... this and the shift immediately ahead would also be a problem afaict, >> which makes me conclude this isn't what Coverity has looked at. I expect >> the problem is with the toolstack side definition of PAGE_SIZE, which imo >> would rather be addressed there. (And yes, I'm pretty averse to arbitrary >> casts like this being introduced.) > > As I've realized while looking at this, wouldn't ma_va_bottom_mask > also better be of type paddr_t, since it's not operating on pfns, but > physical addresses. I didn't adjust the type of ma_va_bottom_mask, > but I would be happy to do it if you agree. No, as its name says it's also used on virtual addresses (really: offsets into the direct map). It hence would better not have any bits set outside of the range that VAs can cover. With that, imo the cast (if any) also should have been to unsigned long, not paddr_t. Yet as said, im the cast would better not be there in the first place. Just that meanwhile I've learned that this was committed already. Jan