From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) (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 357DD1C3BEB; Fri, 3 Apr 2026 01:31:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.133 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775179909; cv=none; b=UWcwNl+zJnBEBO5HQwxt6nxWL7fX5SK4dk+D1ng25+R6sTavpqRc3sma4RbJGr+4ItTo7GbyGGEcYu5vVjTl/nbvCXVF6OyyFZqUOXbFs9whTJveul2y9zAg6P40ZuZ5BgTk8NMAkcCn4MyNXmhdy8pq7lp+wnx0l4obrMnh0AQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775179909; c=relaxed/simple; bh=ui1j+U/lVmdwLQ9xl//b5wqi5bLZ/9P0LsjV28O0GiI=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=C9fMmNV9uYC9dy7kdIX1Cn4/naTSgPJJJ/gYZWrNtOR3KWHTKinv4S6DT9r9XIHR7V3//etyF8o5ZX47Jqsn0CSJyfsQUTvgwxDiVEDGN/JMkJExUgI4ekm/PstinYR4BfrrzRljVpQgTxsrxioOmZMZnXmRzEHExMXtmwCT5z0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=tKaFuDCC; arc=none smtp.client-ip=115.124.30.133 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="tKaFuDCC" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1775179905; h=From:To:Subject:Date:Message-Id:MIME-Version:Content-Type; bh=M+qCrzuXjzCg6dbRyJgE26YGs/aoiqwjPjQvm1evl3o=; b=tKaFuDCCorMU3BGZN52g21QEE6zn6esi+nMFn47RDCqrjWEgIAUpdsQB3f+NiRllEROnTn5I8rl7WdnBxzAJgIoEg5iaCZMLhJ6lH9wdo5nxS98WKHFkQnNZZ3qm1Um3KSWa5Z72DDAacKbI+GLShJSoIa6XDCpGrp8zIt09+cQ= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033032089153;MF=fangyu.yu@linux.alibaba.com;NM=1;PH=DS;RN=18;SR=0;TI=SMTPD_---0X0IV4qf_1775179902; Received: from localhost.localdomain(mailfrom:fangyu.yu@linux.alibaba.com fp:SMTPD_---0X0IV4qf_1775179902 cluster:ay36) by smtp.aliyun-inc.com; Fri, 03 Apr 2026 09:31:43 +0800 From: fangyu.yu@linux.alibaba.com To: anup@brainfault.org Cc: alex@ghiti.fr, andrew.jones@oss.qualcomm.com, aou@eecs.berkeley.edu, atish.patra@linux.dev, corbet@lwn.net, fangyu.yu@linux.alibaba.com, guoren@kernel.org, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, palmer@dabbelt.com, pbonzini@redhat.com, pjw@kernel.org, radim.krcmar@oss.qualcomm.com, skhan@linuxfoundation.org Subject: Re: Re: [PATCH v7 4/4] RISC-V: KVM: add KVM_CAP_RISCV_SET_HGATP_MODE Date: Fri, 3 Apr 2026 09:31:37 +0800 Message-Id: <20260403013137.32604-1-fangyu.yu@linux.alibaba.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit >On Thu, Apr 2, 2026 at 6:53 PM wrote: >> >> From: Fangyu Yu >> >> Add a VM capability that allows userspace to select the G-stage page table >> format by setting HGATP.MODE on a per-VM basis. >> >> Userspace enables the capability via KVM_ENABLE_CAP, passing the requested >> HGATP.MODE in args[0]. The request is rejected with -EINVAL if the mode is >> not supported by the host, and with -EBUSY if the VM has already been >> committed (e.g. vCPUs have been created or any memslot is populated). >> >> KVM_CHECK_EXTENSION(KVM_CAP_RISCV_SET_HGATP_MODE) returns a bitmask of the >> HGATP.MODE formats supported by the host. >> >> Signed-off-by: Fangyu Yu >> Reviewed-by: Andrew Jones >> Reviewed-by: Guo Ren >> --- >> Documentation/virt/kvm/api.rst | 27 +++++++++++++++++++++++++++ >> arch/riscv/kvm/vm.c | 18 ++++++++++++++++-- >> include/uapi/linux/kvm.h | 1 + >> 3 files changed, 44 insertions(+), 2 deletions(-) >> >> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst >> index 032516783e96..9d7f6958fa81 100644 >> --- a/Documentation/virt/kvm/api.rst >> +++ b/Documentation/virt/kvm/api.rst >> @@ -8902,6 +8902,33 @@ helpful if user space wants to emulate instructions which are not >> This capability can be enabled dynamically even if VCPUs were already >> created and are running. >> >> +7.47 KVM_CAP_RISCV_SET_HGATP_MODE >> +--------------------------------- >> + >> +:Architectures: riscv >> +:Type: VM >> +:Parameters: args[0] contains the requested HGATP mode >> +:Returns: >> + - 0 on success. >> + - -EINVAL if args[0] is outside the range of HGATP modes supported by the >> + hardware. >> + - -EBUSY if vCPUs have already been created for the VM, if the VM has any >> + non-empty memslots. >> + >> +This capability allows userspace to explicitly select the HGATP mode for >> +the VM. The selected mode must be supported by both KVM and hardware. This >> +capability must be enabled before creating any vCPUs or memslots. >> + >> +If this capability is not enabled, KVM will select the default HGATP mode >> +automatically. The default is the highest HGATP.MODE value supported by >> +hardware. >> + >> +``KVM_CHECK_EXTENSION(KVM_CAP_RISCV_SET_HGATP_MODE)`` returns a bitmask of >> +HGATP.MODE values supported by the host. A return value of 0 indicates that >> +the capability is not supported. Supported-mode bitmask use HGATP.MODE >> +encodings as defined by the RISC-V privileged specification, such as Sv39x4 >> +corresponds to HGATP.MODE=8, so userspace should test bitmask & BIT(8). >> + >> 8. Other capabilities. >> ====================== >> >> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c >> index 4d82a886102c..5e82a3ad3ad0 100644 >> --- a/arch/riscv/kvm/vm.c >> +++ b/arch/riscv/kvm/vm.c >> @@ -201,6 +201,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) >> case KVM_CAP_VM_GPA_BITS: >> r = kvm_riscv_gstage_gpa_bits(kvm->arch.pgd_levels); >> break; >> + case KVM_CAP_RISCV_SET_HGATP_MODE: >> + r = kvm_riscv_get_hgatp_mode_mask(); >> + break; > >Introducing a new RISC-V capability looks a bit complex. >Instead of KVM_CAP_RISCV_SET_HGATP_MODE, we can >simply re-use KVM_CAP_VM_GPA_BITS. > >The kvm_vm_ioctl_check_extension() for KVM_CAP_VM_GPA_BITS >return number of GPA bits which in-directly implies the underlying >hgatp.MODE. As we know, if it return 59 bits GPA then it means >Sv57x4 is the selected hgatp.MODE and Sv48x4 and Sv39x4 modes >are also supported as-per RISC-V privileged specification. > >The kvm_vm_ioctl_enable_cap() for KVM_CAP_VM_GPA_BITS >will take the desired number of GPA bits and downsize the selected >hgatp.MODE. For example, if user-space ask GPA bits <= 50 and >GPA bits > 41 then we select Sv48x4. If user-space ask GPA >bits <= 41 then we select Sv39x4. If user-space ask GPA bits <= 59 >and GPA bits > 50 then we select Sv57x4. > Thanks, that makes sense. In v8 I’ll drop KVM_CAP_RISCV_SET_HGATP_MODE and re-use KVM_CAP_VM_GPA_BITS for both discovery and selection. Thanks, Fangyu >> default: >> r = 0; >> break; >> @@ -211,12 +214,23 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) >> >> int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap) >> { >> + if (cap->flags) >> + return -EINVAL; >> + >> switch (cap->cap) { >> case KVM_CAP_RISCV_MP_STATE_RESET: >> - if (cap->flags) >> - return -EINVAL; >> kvm->arch.mp_state_reset = true; >> return 0; >> + case KVM_CAP_RISCV_SET_HGATP_MODE: >> + if (!kvm_riscv_hgatp_mode_is_valid(cap->args[0])) >> + return -EINVAL; >> + >> + if (kvm->created_vcpus || !kvm_are_all_memslots_empty(kvm)) >> + return -EBUSY; >> +#ifdef CONFIG_64BIT >> + kvm->arch.pgd_levels = 3 + cap->args[0] - HGATP_MODE_SV39X4; >> +#endif >> + return 0; >> default: >> return -EINVAL; >> } >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> index 80364d4dbebb..a74a80fd4046 100644 >> --- a/include/uapi/linux/kvm.h >> +++ b/include/uapi/linux/kvm.h >> @@ -989,6 +989,7 @@ struct kvm_enable_cap { >> #define KVM_CAP_ARM_SEA_TO_USER 245 >> #define KVM_CAP_S390_USER_OPEREXEC 246 >> #define KVM_CAP_S390_KEYOP 247 >> +#define KVM_CAP_RISCV_SET_HGATP_MODE 248 >> >> struct kvm_irq_routing_irqchip { >> __u32 irqchip; >> -- >> 2.50.1 >> > >Regards, >Anup