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Thu, 28 Aug 2025 02:17:59 -0700 (PDT) Message-ID: <1b9e5d46-20a8-4b5f-b938-e28a0429c770@suse.com> Date: Thu, 28 Aug 2025 11:17:58 +0200 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?= , Jason Andryuk From: Jan Beulich Subject: [PATCH] x86: introduce "hot" and "cold" page copying functions 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: 1756372695444116600 Content-Type: text/plain; charset="utf-8" The present copy_page_sse2() is useful in case the destination page isn't going to get touched again soon, or if we want to limit churn on the caches. Just rename it, to fit the corresponding {clear,scrub}_page_*() naming scheme. For cases where latency is the most important aspect, or when it is expected that sufficiently large parts of a destination page will get accessed again soon after the copying, introduce a "hot" alternative. Again use alternatives patching to select between a "legacy" and an ERMS variant. Don't switch any callers just yet - this will be the subject of subsequent changes. Signed-off-by: Jan Beulich Reviewed-by: Jason Andryuk --- Of course both pages can be independently hot/cold, and hence more flavors may be necessary here. To avoid the NOP padding (also in clear_page_hot()) we could use a double REP prefix in the replacement code (accounting for the REX one in the code being replaced). --- a/xen/arch/x86/copy_page.S +++ b/xen/arch/x86/copy_page.S @@ -13,7 +13,7 @@ #define tmp3_reg %r10 #define tmp4_reg %r11 =20 -FUNC(copy_page_sse2) +FUNC(copy_page_cold) mov $PAGE_SIZE/(4*WORD_SIZE)-3, %ecx =20 prefetchnta 2*4*WORD_SIZE(src_reg) @@ -44,4 +44,19 @@ FUNC(copy_page_sse2) =20 sfence RET -END(copy_page_sse2) +END(copy_page_cold) + + .macro copy_page_movsb + mov $PAGE_SIZE, %ecx + rep movsb + .endm + + .macro copy_page_movsq + mov $PAGE_SIZE/8, %ecx + rep movsq + .endm + +FUNC(copy_page_hot) + ALTERNATIVE copy_page_movsq, copy_page_movsb, X86_FEATURE_ERMS + RET +END(copy_page_hot) --- a/xen/arch/x86/include/asm/page.h +++ b/xen/arch/x86/include/asm/page.h @@ -221,10 +221,11 @@ typedef struct { u64 pfn; } pagetable_t; =20 void clear_page_hot(void *pg); void clear_page_cold(void *pg); -void copy_page_sse2(void *to, const void *from); +void copy_page_hot(void *to, const void *from); +void copy_page_cold(void *to, const void *from); =20 #define clear_page(_p) clear_page_cold(_p) -#define copy_page(_t, _f) copy_page_sse2(_t, _f) +#define copy_page(_t, _f) copy_page_cold(_t, _f) =20 #ifdef CONFIG_DEBUG void scrub_page_hot(void *ptr);