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Tue, 27 Jan 2026 05:21:01 -0800 (PST) Message-ID: <7982a813-0fda-447e-a0f1-c9357b85f264@suse.com> Date: Tue, 27 Jan 2026 14:20:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US To: "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= From: Jan Beulich Subject: [PATCH] x86/shadow: suppress trace_emul_write_val hook when !TRACEBUFFER 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 Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @suse.com) X-ZM-MESSAGEID: 1769520078812154100 Content-Type: text/plain; charset="utf-8" The hook is never invoked in that case, and hence needlessly offers an extra valid indirect call target. With the hook suppressed, no consumer of the three local per-CPU variables exists either, so they're suppressed as well. Signed-off-by: Jan Beulich --- a/xen/arch/x86/include/asm/paging.h +++ b/xen/arch/x86/include/asm/paging.h @@ -90,10 +90,12 @@ struct shadow_paging_mode { int (*guess_wrmap )(struct vcpu *v,=20 unsigned long vaddr, mfn_t gmf= n); void (*pagetable_dying )(paddr_t gpa); +#ifdef CONFIG_TRACEBUFFER void (*trace_emul_write_val )(const void *ptr, unsigned long= vaddr, const void *src, unsigned int = bytes); #endif #endif +#endif /* For outsiders to tell what mode we're in */ unsigned int shadow_levels; }; --- a/xen/arch/x86/mm/shadow/hvm.c +++ b/xen/arch/x86/mm/shadow/hvm.c @@ -211,9 +211,11 @@ hvm_emulate_write(enum x86_segment seg, default: memcpy(ptr, p_data, bytes); break; } =20 +#ifdef CONFIG_TRACEBUFFER if ( tb_init_done ) v->arch.paging.mode->shadow.trace_emul_write_val(ptr, addr, p_data, bytes); +#endif =20 sh_emulate_unmap_dest(v, ptr, bytes, sh_ctxt); shadow_audit_tables(v); --- a/xen/arch/x86/mm/shadow/multi.c +++ b/xen/arch/x86/mm/shadow/multi.c @@ -2044,6 +2044,7 @@ static void __maybe_unused sh_trace_gfn_ } =20 #ifdef CONFIG_HVM +#ifdef CONFIG_TRACEBUFFER #if GUEST_PAGING_LEVELS =3D=3D 3 static DEFINE_PER_CPU(guest_va_t,trace_emulate_initial_va); static DEFINE_PER_CPU(int,trace_extra_emulation_count); @@ -2071,9 +2072,11 @@ static void cf_check trace_emulate_write memcpy(&this_cpu(trace_emulate_write_val), src, bytes); #endif } +#endif /* CONFIG_TRACEBUFFER */ =20 static inline void sh_trace_emulate(guest_l1e_t gl1e, unsigned long va) { +#ifdef CONFIG_TRACEBUFFER if ( tb_init_done ) { struct __packed { @@ -2099,6 +2102,7 @@ static inline void sh_trace_emulate(gues =20 sh_trace(TRC_SHADOW_EMULATE, sizeof(d), &d); } +#endif /* CONFIG_TRACEBUFFER */ } #endif /* CONFIG_HVM */ =20 @@ -2678,7 +2682,9 @@ static int cf_check sh_page_fault( paging_unlock(d); put_gfn(d, gfn_x(gfn)); =20 +#ifdef CONFIG_TRACEBUFFER this_cpu(trace_emulate_write_val) =3D (guest_l1e_t){}; +#endif =20 #if SHADOW_OPTIMIZATIONS & SHOPT_FAST_EMULATION early_emulation: @@ -2794,7 +2800,10 @@ static int cf_check sh_page_fault( if ( r =3D=3D X86EMUL_OKAY && !emul_ctxt.ctxt.retire.raw ) { int i, emulation_count=3D0; + +#ifdef CONFIG_TRACEBUFFER this_cpu(trace_emulate_initial_va) =3D va; +#endif =20 for ( i =3D 0 ; i < 4 ; i++ ) { @@ -2830,7 +2839,10 @@ static int cf_check sh_page_fault( break; /* Don't emulate again if we failed! */ } } + +#ifdef CONFIG_TRACEBUFFER this_cpu(trace_extra_emulation_count)=3Demulation_count; +#endif } #endif /* PAE guest */ =20 @@ -4130,7 +4142,9 @@ const struct paging_mode sh_paging_mode .shadow.guess_wrmap =3D sh_guess_wrmap, #endif .shadow.pagetable_dying =3D sh_pagetable_dying, +#ifdef CONFIG_TRACEBUFFER .shadow.trace_emul_write_val =3D trace_emulate_write_val, +#endif #endif /* CONFIG_HVM */ .shadow.shadow_levels =3D SHADOW_PAGING_LEVELS, };