From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 178D130566F for ; Thu, 4 Jun 2026 03:04:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.19 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780542273; cv=none; b=dOpJpgdvsj/9hdZcsopni26PK7aMUW3ib3mcGf8xsfee3HcSvbdB376zjOjBjlBEUy9NGLFHKwAQQXDvkwyv40FLg4ozX3daCTgOvGgEdC5r/U3O5ujXZcQLJN7GyhacgUBrlt+fLD8QSRB9QO1P4zMaJmShGbvS2qI5XR+AzHw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780542273; c=relaxed/simple; bh=7IrbNTGaHeKOVrxzFjq7meMvrGXDzTJWWuaUASD7OJ8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KWqb/t+cgPPKIHnOtqDxmuEeZG8NU1oYpIbcnCWJPIPRm0SzSuYx7r/LVxKhDu1fm1oerjsiJmXCDz7hELrHAs+z2C0s580lYSOTGLt9QuLZSBa6v9OuDltu7TmqGu9mRiD2OPRMEd7lMToWvnGn5E5ltOJJc7t22R350i/NsOY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=av06XMAT; arc=none smtp.client-ip=192.198.163.19 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="av06XMAT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1780542272; x=1812078272; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=7IrbNTGaHeKOVrxzFjq7meMvrGXDzTJWWuaUASD7OJ8=; b=av06XMATCep2XJe1naYDrua8Go1IHWRUHomAc7uu1ZKBpVucgnkmZ9q2 R3VEp3r1anJLV4BYOHhwqrQ8bOHHcT9DlGT2C3BdVdFogEQEEZ4nZjQR/ AIhqEkRJ/P/fzj53K0vcGF5kdYgu/ULaVXXocKRNAOZ6lB8k1TF0ielgi CF0bbatD9RmdckGPmJG0t6WEZWgiJUH8UDv+uzLlHcZUPde6Q8zYag1hK zwjMmPU2ds6tlE+MSxO7W2jM6WW5zh2nNqEs1/3PYzlCao+jLtyisMDDq o7NcUmDCHh9cIIB2hB7niTviWnlJjtfrrIF/+T7oDnNYDQaZFlYT4fiI1 Q==; X-CSE-ConnectionGUID: yE5DPwpyT1eH8ykl8ZlIhg== X-CSE-MsgGUID: bgsgd7OcSzqEXQnjMrr+Iw== X-IronPort-AV: E=McAfee;i="6800,10657,11806"; a="80399647" X-IronPort-AV: E=Sophos;i="6.24,186,1774335600"; d="scan'208";a="80399647" Received: from fmviesa008.fm.intel.com ([10.60.135.148]) by fmvoesa113.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Jun 2026 20:04:29 -0700 X-CSE-ConnectionGUID: R55l5KQNT7ujpkmLghg67g== X-CSE-MsgGUID: 17oPsdMmRqCpBHtIAuf1yg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.24,186,1774335600"; d="scan'208";a="241915849" Received: from 9cc2c43eec6b.jf.intel.com ([10.54.77.29]) by fmviesa008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Jun 2026 20:04:28 -0700 From: Zide Chen To: qemu-devel@nongnu.org, kvm@vger.kernel.org, Paolo Bonzini , Zhao Liu , Peter Xu , Fabiano Rosas , Sandipan Das Cc: Xiaoyao Li , Dongli Zhang , Dapeng Mi , Zide Chen Subject: [PATCH v4 5/6] target/i386: Increase MSR_BUF_SIZE and split KVM_[GET/SET]_MSRS calls Date: Wed, 3 Jun 2026 19:55:45 -0700 Message-ID: <20260604025546.19378-6-zide.chen@intel.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260604025546.19378-1-zide.chen@intel.com> References: <20260604025546.19378-1-zide.chen@intel.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Newer Intel server CPUs support a large number of PMU MSRs. Currently, QEMU allocates cpu->kvm_msr_buf as a single-page buffer, which is not sufficient to hold all possible MSRs. Increase MSR_BUF_SIZE to 8192 bytes, providing space for up to 511 MSRs. This is sufficient even for the theoretical worst case, such as architectural LBR with a depth of 64. KVM_[GET/SET]_MSRS is limited to 255 MSRs per call. Raising this limit to 511 would require changes in KVM and would introduce backward compatibility issues. Instead, split requests into multiple KVM_[GET/SET]_MSRS calls when the number of MSRs exceeds the API limit. Reviewed-by: Dapeng Mi Signed-off-by: Zide Chen --- v4: - Add assert on kvm_init_msrs() to catch the error of KVM_SET_MSRS has negative return. v3: - Address Dapeng's comments. --- target/i386/kvm/kvm.c | 110 +++++++++++++++++++++++++++++++++++------- 1 file changed, 92 insertions(+), 18 deletions(-) diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index a99c1dba83f2..9b6407794e43 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -97,9 +97,12 @@ #define KVM_APIC_BUS_CYCLE_NS 1 #define KVM_APIC_BUS_FREQUENCY (1000000000ULL / KVM_APIC_BUS_CYCLE_NS) -/* A 4096-byte buffer can hold the 8-byte kvm_msrs header, plus - * 255 kvm_msr_entry structs */ -#define MSR_BUF_SIZE 4096 +/* An 8192-byte buffer can hold the 8-byte kvm_msrs header, plus + * 511 kvm_msr_entry structs */ +#define MSR_BUF_SIZE 8192 + +/* Maximum number of MSRs in one single KVM_[GET/SET]_MSRS call. */ +#define KVM_MAX_IO_MSRS 255 typedef bool QEMURDMSRHandler(X86CPU *cpu, uint32_t msr, uint64_t *val); typedef bool QEMUWRMSRHandler(X86CPU *cpu, uint32_t msr, uint64_t val); @@ -4099,21 +4102,99 @@ static void kvm_msr_entry_add_perf(X86CPU *cpu, FeatureWordArray f) } } -static int kvm_buf_set_msrs(X86CPU *cpu) +static int __kvm_buf_set_msrs(X86CPU *cpu, struct kvm_msrs *msrs) { - int ret = kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, cpu->kvm_msr_buf); + int ret = kvm_vcpu_ioctl(CPU(cpu), KVM_SET_MSRS, msrs); if (ret < 0) { return ret; } - if (ret < cpu->kvm_msr_buf->nmsrs) { - struct kvm_msr_entry *e = &cpu->kvm_msr_buf->entries[ret]; + if (ret < msrs->nmsrs) { + struct kvm_msr_entry *e = &msrs->entries[ret]; error_report("error: failed to set MSR 0x%" PRIx32 " to 0x%" PRIx64, (uint32_t)e->index, (uint64_t)e->data); } - assert(ret == cpu->kvm_msr_buf->nmsrs); - return 0; + assert(ret == msrs->nmsrs); + return ret; +} + +static int __kvm_buf_get_msrs(X86CPU *cpu, struct kvm_msrs *msrs) +{ + int ret; + + ret = kvm_vcpu_ioctl(CPU(cpu), KVM_GET_MSRS, msrs); + if (ret < 0) { + return ret; + } + + if (ret < msrs->nmsrs) { + struct kvm_msr_entry *e = &msrs->entries[ret]; + error_report("error: failed to get MSR 0x%" PRIx32, + (uint32_t)e->index); + } + + assert(ret == msrs->nmsrs); + return ret; +} + +static int kvm_buf_set_or_get_msrs(X86CPU *cpu, bool is_write) +{ + struct kvm_msr_entry *entries = cpu->kvm_msr_buf->entries; + struct kvm_msrs *buf = NULL; + int current, remaining, ret = 0; + size_t buf_size; + + buf_size = KVM_MAX_IO_MSRS * sizeof(struct kvm_msr_entry) + + sizeof(struct kvm_msrs); + buf = g_malloc(buf_size); + + remaining = cpu->kvm_msr_buf->nmsrs; + current = 0; + while (remaining) { + size_t size; + + memset(buf, 0, buf_size); + + if (remaining > KVM_MAX_IO_MSRS) { + buf->nmsrs = KVM_MAX_IO_MSRS; + } else { + buf->nmsrs = remaining; + } + + size = buf->nmsrs * sizeof(entries[0]); + memcpy(buf->entries, &entries[current], size); + + if (is_write) { + ret = __kvm_buf_set_msrs(cpu, buf); + } else { + ret = __kvm_buf_get_msrs(cpu, buf); + } + + if (ret < 0) { + goto out; + } + + if (!is_write) + memcpy(&entries[current], buf->entries, size); + + current += buf->nmsrs; + remaining -= buf->nmsrs; + } + +out: + g_free(buf); + return ret < 0 ? ret : cpu->kvm_msr_buf->nmsrs; +} + +static inline int kvm_buf_set_msrs(X86CPU *cpu) +{ + return kvm_buf_set_or_get_msrs(cpu, true); +} + +static inline int kvm_buf_get_msrs(X86CPU *cpu) +{ + return kvm_buf_set_or_get_msrs(cpu, false); } static void kvm_init_msrs(X86CPU *cpu) @@ -4149,7 +4230,7 @@ static void kvm_init_msrs(X86CPU *cpu) if (has_msr_ucode_rev) { kvm_msr_entry_add(cpu, MSR_IA32_UCODE_REV, cpu->ucode_rev); } - assert(kvm_buf_set_msrs(cpu) == 0); + assert(kvm_buf_set_msrs(cpu) == cpu->kvm_msr_buf->nmsrs); } static int kvm_put_msrs(X86CPU *cpu, KvmPutState level) @@ -5042,18 +5123,11 @@ static int kvm_get_msrs(X86CPU *cpu) } } - ret = kvm_vcpu_ioctl(CPU(cpu), KVM_GET_MSRS, cpu->kvm_msr_buf); + ret = kvm_buf_get_msrs(cpu); if (ret < 0) { return ret; } - if (ret < cpu->kvm_msr_buf->nmsrs) { - struct kvm_msr_entry *e = &cpu->kvm_msr_buf->entries[ret]; - error_report("error: failed to get MSR 0x%" PRIx32, - (uint32_t)e->index); - } - - assert(ret == cpu->kvm_msr_buf->nmsrs); /* * MTRR masks: Each mask consists of 5 parts * a 10..0: must be zero -- 2.54.0