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Smith" , "xen-devel@lists.xenproject.org" , Tamas K Lengyel References: <20251013101540.3502842-1-Penny.Zheng@amd.com> <20251013101540.3502842-10-Penny.Zheng@amd.com> <1a9ac91c-2295-4749-8807-668fcecf8f8e@suse.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: 7bit On 11.11.2025 08:08, Penny, Zheng wrote: > [Public] > > Hi, > > Sorry for the late response. Just got back from long annual leaves > >> -----Original Message----- >>> --- a/xen/arch/x86/include/asm/mem_access.h >>> +++ b/xen/arch/x86/include/asm/mem_access.h >>> @@ -14,6 +14,7 @@ >>> #ifndef __ASM_X86_MEM_ACCESS_H__ >>> #define __ASM_X86_MEM_ACCESS_H__ >>> >>> +#ifdef CONFIG_VM_EVENT >>> /* >>> * Setup vm_event request based on the access (gla is -1ull if not available). >>> * Handles the rw2rx conversion. Boolean return value indicates if event type >>> @@ -25,6 +26,14 @@ >>> bool p2m_mem_access_check(paddr_t gpa, unsigned long gla, >>> struct npfec npfec, >>> struct vm_event_st **req_ptr); >>> +#else >>> +static inline bool p2m_mem_access_check(paddr_t gpa, unsigned long gla, >>> + struct npfec npfec, >>> + struct vm_event_st **req_ptr) >>> +{ >>> + return false; >> >> Leaving *req_ptr untouched feels dangerous; the fact that the sole caller has >> what it uses set to NULL up front is secondary. >> > > If we *req_ptr = NULL; compiler will not DCE the following code block when VM_EVENT=n: > ``` > if ( req_ptr ) > { > if ( monitor_traps(curr, sync, req_ptr) < 0 ) > rc = 0; > > xfree(req_ptr); > } > return rc; > ``` > Or am I misunderstanding what you suggest? First: It would have helped if you had also said where that code fragment actually was taken from. Seeing it's in hvm_hap_nested_page_fault(), I'm having trouble following why the compiler wouldn't be able to see that the local variable "req_ptr" there would never change value, i.e. remain NULL throughout its lifetime. If indeed there's a compiler shortcoming, that either wants working around or properly writing down. Jan