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Mon, 21 Sep 2026 01:59:02 -0700 (PDT) Message-ID: Date: Mon, 21 Sep 2026 10:59:09 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] x86/pagewalk: avoid ACCESS_ONCE() in compound literals To: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= Cc: "xen-devel@lists.xenproject.org" , Nicola Vetrini , Andrew Cooper , Teddy Astie References: 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 X-purgate-ID: tlsNG-ef75cf/1789981143-364DBAE4-31F6FB70/0/0 X-purgate-type: clean X-purgate-size: 1411 On 21.09.2026 10:53, Roger Pau Monné wrote: > On Thu, Sep 03, 2026 at 01:51:28PM +0200, Jan Beulich wrote: >> Compound literals are also covered by Misra C:2012 rule 13.1 >> ("Initializer lists shall not contain persistent side effects"), and >> (sadly?) that rule also applies to lists with just a single element, or >> more generally with just a single side effect. Use intermediate variables >> to overcome this as well as ACCESS_ONCE()'s restriction to be usable on >> scalar types only. >> >> No functional change intended. >> >> Fixes: 0345b835dc97 ("x86/pagewalk: Read guest PTEs with ACCESS_ONCE()") >> Signed-off-by: Jan Beulich >> >> --- a/xen/arch/x86/mm/guest_walk.c >> +++ b/xen/arch/x86/mm/guest_walk.c >> @@ -129,7 +129,9 @@ guest_walk_tables(const struct vcpu *v, >> guest_l4_table_offset(va) * sizeof(gw->l4e); >> if ( !hvmemul_read_cache(v, l4gpa, &gw->l4e, sizeof(gw->l4e)) ) >> { >> - gw->l4e = (guest_l4e_t){ ACCESS_ONCE(l4p[guest_l4_table_offset(va)].l4) }; >> + guest_intpte_t l4e = ACCESS_ONCE(l4p[guest_l4_table_offset(va)].l4); >> + >> + gw->l4e = (guest_l4e_t){ l4e }; > > Did you consider using the l4e_from_intpte() and similar helpers here > and below? No, I didn't, as they aren't applicable to guest_le_t. guest_intpte_t aliases intpte_t only for GUEST_PAGING_LEVELS > 2. Jan