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X-IronPort-AV: E=McAfee;i="6600,9927,10892"; a="421469911" X-IronPort-AV: E=Sophos;i="6.03,298,1694761200"; d="scan'208";a="421469911" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Nov 2023 19:37:22 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10892"; a="764228152" X-IronPort-AV: E=Sophos;i="6.03,298,1694761200"; d="scan'208";a="764228152" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.93.6.77]) ([10.93.6.77]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Nov 2023 19:37:09 -0800 Message-ID: Date: Mon, 13 Nov 2023 11:37:05 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 15/34] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory To: Sean Christopherson Cc: Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , David Matlack , Yu Zhang , Isaku Yamahata , =?UTF-8?B?TWlja2HDq2wgU2FsYcO8?= =?UTF-8?Q?n?= , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A. Shutemov" References: <20231105163040.14904-1-pbonzini@redhat.com> <20231105163040.14904-16-pbonzini@redhat.com> <956d8ee3-8b63-4a2d-b0c4-c0d3d74a0f6f@intel.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: 973id7egngmc5qqik4f9n3puguscrf8c X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E89C140007 X-HE-Tag: 1699846643-975326 X-HE-Meta: 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 7mEgTNMw JJOiazh0hXHAmAGmgtC947SCPkE1tzMkAkH45M6K4E2NpXIsO1CUDvYtgsULbP/Bd4fxlqK7MdzlRMDFpV0Rbp6OnxDNFsSXEYd1n5/pzEMtRzH7ovN9xddO3FiBV1wF9C0jqDw5BhneeH0TXosZzpVKKoU9yyDhdegGs4IEcTg5hhYcnAU8u1md6jGzoMSXnfK/HaCc0ovj1dudDxurzYQ9DKHJTY960EqfvLWRv90E+YPWeCzRVh2Cx6qbrBEomvWYYH6heFuQA/A98Ph6tgvyNMffH4hLjl9PNcrUSuyZAnNY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/11/2023 2:22 AM, Sean Christopherson wrote: > On Fri, Nov 10, 2023, Xiaoyao Li wrote: >> On 11/6/2023 12:30 AM, Paolo Bonzini wrote: >>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >>> index 68a144cb7dbc..a6de526c0426 100644 >>> --- a/include/linux/kvm_host.h >>> +++ b/include/linux/kvm_host.h >>> @@ -589,8 +589,20 @@ struct kvm_memory_slot { >>> u32 flags; >>> short id; >>> u16 as_id; >>> + >>> +#ifdef CONFIG_KVM_PRIVATE_MEM >>> + struct { >>> + struct file __rcu *file; >>> + pgoff_t pgoff; >>> + } gmem; >>> +#endif >>> }; >>> +static inline bool kvm_slot_can_be_private(const struct kvm_memory_slot *slot) >>> +{ >>> + return slot && (slot->flags & KVM_MEM_GUEST_MEMFD); >>> +} >>> + >> >> maybe we can move this block and ... >> >> >> >>> @@ -2355,6 +2379,30 @@ bool kvm_arch_pre_set_memory_attributes(struct kvm *kvm, >>> struct kvm_gfn_range *range); >>> bool kvm_arch_post_set_memory_attributes(struct kvm *kvm, >>> struct kvm_gfn_range *range); >>> + >>> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) >>> +{ >>> + return IS_ENABLED(CONFIG_KVM_PRIVATE_MEM) && >>> + kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE; >>> +} >>> +#else >>> +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn) >>> +{ >>> + return false; >>> +} >>> #endif /* CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES */ >> >> this block to Patch 18? > > It would work, but my vote is to keep them here to minimize the changes to common > KVM code in the x86 enabling. It's not a strong preference though. Of course, > at this point, fiddling with this sort of thing is probably a bad idea in terms > of landing guest_memfd. Indeed. It's OK then. >>> @@ -4844,6 +4875,10 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) >>> #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES >>> case KVM_CAP_MEMORY_ATTRIBUTES: >>> return kvm_supported_mem_attributes(kvm); >>> +#endif >>> +#ifdef CONFIG_KVM_PRIVATE_MEM >>> + case KVM_CAP_GUEST_MEMFD: >>> + return !kvm || kvm_arch_has_private_mem(kvm); >>> #endif >>> default: >>> break; >>> @@ -5277,6 +5312,18 @@ static long kvm_vm_ioctl(struct file *filp, >>> case KVM_GET_STATS_FD: >>> r = kvm_vm_ioctl_get_stats_fd(kvm); >>> break; >>> +#ifdef CONFIG_KVM_PRIVATE_MEM >>> + case KVM_CREATE_GUEST_MEMFD: { >>> + struct kvm_create_guest_memfd guest_memfd; >> >> Do we need a guard of below? >> >> r = -EINVAL; >> if (!kvm_arch_has_private_mem(kvm)) >> goto out; > > Argh, yeah, that's weird since KVM_CAP_GUEST_MEMFD says "not supported" if the > VM doesn't support private memory. > > Enforcing that would break guest_memfd_test.c though. And having to create a > "special" VM just to test basic guest_memfd functionality would be quite > annoying. > > So my vote is to do: > > case KVM_CAP_GUEST_MEMFD: > return IS_ENABLED(CONFIG_KVM_PRIVATE_MEM); I'm fine with it. > There's no harm to KVM if userspace creates a file it can't use, and at some > point KVM will hopefully support guest_memfd irrespective of private memory.