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[37.24.206.209]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5c882494863sm4536246a12.92.2024.09.30.08.08.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 Sep 2024 08:08:17 -0700 (PDT) X-Outflank-Mailman: Message body and most headers restored to incoming version X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d3749afa-7f3d-11ef-99a2-01e77a169b0f DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1727708898; x=1728313698; darn=lists.xenproject.org; h=content-transfer-encoding:autocrypt:subject:from:cc:to :content-language:user-agent:mime-version:date:message-id:from:to:cc :subject:date:message-id:reply-to; bh=iI9UhhIP46ohbqpT7wPLqw3ghHjlTKT7Zx5OV6H10J8=; b=Gx/DGs4aksPihJG73KRCqwlhvNPBz3rUtitnflYkIADoxTTzOC/sAu/ohFFbZ+DV+b JyoSiw41N4qxP2SsPNePdyTrA7OTXFTAXIYi29rHY2h0HXXk3tT4Kf3KnFGaaHc5J9Gj Arl50MCQ2W7CIRUdMnajWDtNu2GTA7Lxt77aMYjQgDM3Z+Lnkei/rSxH+k4RUfqCVBvb 7hlgSnRpPV7ZP+6ACZY7L1pF9A7rkdSTR2wwLLU9hmiyq536VL8dEubnSK2vRqSJs+Bp MV+4XiADtUJ92oeyq8A2YRYrLWI1Q3RYA5eQUqs+1fEJqxEO+axeCZdPjUn6ACFRjuby 2RDg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1727708898; x=1728313698; h=content-transfer-encoding:autocrypt:subject:from:cc:to :content-language:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=iI9UhhIP46ohbqpT7wPLqw3ghHjlTKT7Zx5OV6H10J8=; b=ntBu0Xd6oKz6Xg2YMXuXxRH3UMVDOMLfe2ijBchL893ywn535ZOeAoNNcN1mvdiX1j DnYH1wh4GQtZT4BsRFIMKwVoJxtpvwNuXxXNvstf2D0ccyqfC/gJkQ5kz3LW4hNLfInn 9s9i7dBRflYDEYL0jOHJvmi0z+5D/AZ6/MDEtfjNXSCncY1CwfttIV11DVJBUKtELo+N EVS6ZIys8xRt3bZ/kPPBFvr2ettWzWVLNmrGXU93ba8giCtO+a+iTOOynudJrqQFpmkk OAbjGCYAsOK5CT3ztNnRJsG8zz0p5P7cm+p49LySH5hQKaxAZr4NJf+/iDdjmn6V5xPl R9KQ== X-Gm-Message-State: AOJu0YzcIar8IjYSwjMFC7SsCUXl4FAM8wrMQTEZ9MTiSJ6mLx4Z89Oi L2cq+iAR92ju1wcPnqfx7FdW7os7V6s9mfy9cYSyXLihDABFpfymO8bArksUscjztwjcVshLX6g = X-Google-Smtp-Source: AGHT+IFrnI3xsbgon9Ga4ryiqyTMdH9+aIS4v4fWBkwVtcQ+4Z1RJ59HDLgI+YV+M9Hy/CYG+iSwpw== X-Received: by 2002:a2e:be1c:0:b0:2fa:cd3d:4a76 with SMTP id 38308e7fff4ca-2facd3d4c8fmr30686311fa.43.1727708898203; Mon, 30 Sep 2024 08:08:18 -0700 (PDT) Message-ID: Date: Mon, 30 Sep 2024 17:08:17 +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?= From: Jan Beulich Subject: [PATCH] x86: prefer RDTSCP in rdtsc_ordered() 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: 1727708942526116600 Content-Type: text/plain; charset="utf-8" If available, its use is supposed to be cheaper than LFENCE+RDTSC, and is virtually guaranteed to be cheaper than MFENCE+RDTSC. Unlike in rdtsc() use 64-bit local variables, eliminating the need for the compiler to emit a zero-extension insn for %eax (that's a cheap MOV, yet still pointless to have). Suggested-by: Andrew Cooper Signed-off-by: Jan Beulich --- a/xen/arch/x86/include/asm/msr.h +++ b/xen/arch/x86/include/asm/msr.h @@ -108,18 +108,30 @@ static inline uint64_t rdtsc(void) =20 static inline uint64_t rdtsc_ordered(void) { - /* - * The RDTSC instruction is not ordered relative to memory access. - * The Intel SDM and the AMD APM are both vague on this point, but - * empirically an RDTSC instruction can be speculatively executed - * before prior loads. An RDTSC immediately after an appropriate - * barrier appears to be ordered as a normal load, that is, it - * provides the same ordering guarantees as reading from a global - * memory location that some other imaginary CPU is updating - * continuously with a time stamp. - */ - alternative("lfence", "mfence", X86_FEATURE_MFENCE_RDTSC); - return rdtsc(); + uint64_t low, high, aux; + + /* + * The RDTSC instruction is not ordered relative to memory access. + * The Intel SDM and the AMD APM are both vague on this point, but + * empirically an RDTSC instruction can be speculatively executed + * before prior loads. An RDTSC immediately after an appropriate + * barrier appears to be ordered as a normal load, that is, it + * provides the same ordering guarantees as reading from a global + * memory location that some other imaginary CPU is updating + * continuously with a time stamp. + * + * RDTSCP, otoh, "does wait until all previous instructions have + * executed and all previous loads are globally visible" (SDM) / + * "forces all older instructions to retire before reading the + * timestamp counter" (APM) + */ + alternative_io_2("lfence; rdtsc", + "mfence; rdtsc", X86_FEATURE_MFENCE_RDTSC, + "rdtscp", X86_FEATURE_RDTSCP, + ASM_OUTPUT2("=3Da" (low), "=3Dd" (high), "=3Dc" (aux)= ), + /* no inputs */); + + return (high << 32) | low; } =20 #define __write_tsc(val) wrmsrl(MSR_IA32_TSC, val)