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AJvYcCXeVFd9ITeMSheItezN/fr4AoH2mb1+y/MsPDcEQNJIXCWQrc3JckEj1B3ElflsdB1NNncehONBSDc=@vger.kernel.org X-Gm-Message-State: AOJu0YxwfLe1wPJdy3asJQURh6TF3ItuagoxK9Pb02ccYgnjTjhjetlk h5zE5Q1GVFS15uIzsfdC1Ilf+HO+Z9O6olCJLzadTCC/isBjHLLRHNv+yre+3JXOssu6mWPLa5w zPQ== X-Google-Smtp-Source: AGHT+IGedxc9J5DHeJSE9G0tqfkTa1UlOm8+kBbsCPW2uqNOUB/tlH2c/Ts0LAuodf0hiT+LMDCf9z19zLQ= X-Received: from pjbqo4.prod.google.com ([2002:a17:90b:3dc4:b0:2fa:1fac:2695]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2dc3:b0:2ff:4a8d:74f9 with SMTP id 98e67ed59e1d1-309ee39aa1dmr3821199a91.10.1745502170041; Thu, 24 Apr 2025 06:42:50 -0700 (PDT) Date: Thu, 24 Apr 2025 06:42:48 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: linux-sgx@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250415115213.291449-1-elena.reshetova@intel.com> <20250415115213.291449-3-elena.reshetova@intel.com> Message-ID: Subject: Re: [PATCH v3 2/2] x86/sgx: Implement EUPDATESVN and opportunistically call it during first EPC page alloc From: Sean Christopherson To: Elena Reshetova Cc: Kai Huang , Dave Hansen , "linux-sgx@vger.kernel.org" , Vincent R Scarlata , "x86@kernel.org" , "jarkko@kernel.org" , Vishal Annapurve , Chong Cai , Asit K Mallick , Erdem Aktas , "linux-kernel@vger.kernel.org" , "bondarn@google.com" , "dionnaglaze@google.com" , Scott Raynor Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Thu, Apr 24, 2025, Elena Reshetova wrote: > > On Tue, Apr 22, 2025, Kai Huang wrote: > > > On Fri, 2025-04-18 at 07:55 -0700, Sean Christopherson wrote: > > > > On Tue, Apr 15, 2025, Elena Reshetova wrote: > > > > That said, handling this deep in the bowels of EPC page allocation = seems > > > > unnecessary. The only way for there to be no active EPC pages is i= f > > > > there are no enclaves. As above, virtual EPC usage is already all = but > > > > guaranteed to hit false positives, so I don't think there's anythin= g > > > > gained by trying to update the SVN based on EPC allocations. > > > > > > > > So rather than react to EPC allocations, why not hook sgx_open() an= d > > sgx_vepc_open()? > > > > > > The only thing I don't like about this is we need to hook both of the= m. > >=20 > > And having to maintain a separate counter. ... > If we follow the approach of trying to execute EUPDATESVN via=20 > sgx_open() and sgx_vepc_open() paths, it adds more complexity to kernel > code=20 This is where I disagree. I don't see how it's more complex even on the su= rface, and when you start considering the implications of "randomly" inserting a n= on- trivial operation into EPC allocation, IMO it's far less complex overall. > and imo it still doesn=E2=80=99t remove the complexity from userspace > orchestration sw. I.e. userspace still has to get rid of host enclaves an= d=20 > SGX enabled VMs (because syncing with VMs owners to make sure their > encalves are destroyed and these VMs are ready for EUDPATESVN seems > like a big organizational complexity and error prone). Yeah, I don't see a way around that. > So, the only thing this approach would address would be an EPC > pre-allocation done by qemu? Wouldn't it be more reasonable > (here I am purely speculating, I dont know qemu code) to implement > in qemu the code to drop EPC pre-allocation if no VMs with SGX are > running? That would be a good overall policy imo not to waste EPC > space when not needed in practice.=20 QEMU only preallocates when the VM is being created, i.e. QEMU doesn't main= tain a persistent pool. All I was saying is that userspace needs to shut down S= GX capable VMs, even if the VM isn't actively running enclaves, which is a sha= me. Untested sketch of hooking create/delete to do SVN updates. --- arch/x86/kernel/cpu/sgx/driver.c | 4 ++++ arch/x86/kernel/cpu/sgx/encl.c | 2 ++ arch/x86/kernel/cpu/sgx/main.c | 34 ++++++++++++++++++++++++++++++++ arch/x86/kernel/cpu/sgx/sgx.h | 3 +++ arch/x86/kernel/cpu/sgx/virt.c | 6 ++++++ 5 files changed, 49 insertions(+) diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/dri= ver.c index 7f8d1e11dbee..669e44d61f9f 100644 --- a/arch/x86/kernel/cpu/sgx/driver.c +++ b/arch/x86/kernel/cpu/sgx/driver.c @@ -19,6 +19,10 @@ static int sgx_open(struct inode *inode, struct file *fi= le) struct sgx_encl *encl; int ret; =20 + ret =3D sgx_inc_usage_count(); + if (ret) + return ret; + encl =3D kzalloc(sizeof(*encl), GFP_KERNEL); if (!encl) return -ENOMEM; diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.= c index 279148e72459..84ca78627e55 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -765,6 +765,8 @@ void sgx_encl_release(struct kref *ref) WARN_ON_ONCE(encl->secs.epc_page); =20 kfree(encl); + + sgx_dec_usage_count(); } =20 /* diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.= c index 8ce352fc72ac..ca74c91d4291 100644 --- a/arch/x86/kernel/cpu/sgx/main.c +++ b/arch/x86/kernel/cpu/sgx/main.c @@ -914,6 +914,40 @@ int sgx_set_attribute(unsigned long *allowed_attribute= s, } EXPORT_SYMBOL_GPL(sgx_set_attribute); =20 +static atomic_t sgx_usage_count; +static DEFINE_MUTEX(sgx_svn_lock); + +static int sgx_update_svn(void) +{ + // blah blah blah +} + +int sgx_inc_usage_count(void) +{ + if (atomic_inc_not_zero(&sgx_usage_count)) + return 0; + + guard(mutex)(&sgx_svn_lock); + + if (atomic_inc_not_zero(&sgx_usage_count)) + return 0; + + return sgx_update_svn(); +} + +void sgx_dec_usage_count(void) +{ + if (atomic_dec_return(&sgx_usage_count)) + return; + + guard(mutex)(&sgx_svn_lock); + + if (atomic_read(&sgx_usage_count)) + return; + + sgx_update_svn(); +} + static int __init sgx_init(void) { int ret; diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h index d2dad21259a8..f5940393d9bd 100644 --- a/arch/x86/kernel/cpu/sgx/sgx.h +++ b/arch/x86/kernel/cpu/sgx/sgx.h @@ -102,6 +102,9 @@ static inline int __init sgx_vepc_init(void) } #endif =20 +int sgx_inc_usage_count(void); +void sgx_dec_usage_count(void); + void sgx_update_lepubkeyhash(u64 *lepubkeyhash); =20 #endif /* _X86_SGX_H */ diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.= c index 7aaa3652e31d..e548de340c2e 100644 --- a/arch/x86/kernel/cpu/sgx/virt.c +++ b/arch/x86/kernel/cpu/sgx/virt.c @@ -255,12 +255,18 @@ static int sgx_vepc_release(struct inode *inode, stru= ct file *file) xa_destroy(&vepc->page_array); kfree(vepc); =20 + sgx_dec_usage_count(); return 0; } =20 static int sgx_vepc_open(struct inode *inode, struct file *file) { struct sgx_vepc *vepc; + int ret; + + ret =3D sgx_inc_usage_count(); + if (ret) + return ret; =20 vepc =3D kzalloc(sizeof(struct sgx_vepc), GFP_KERNEL); if (!vepc) base-commit: 37374f38f6c5291ae66ce05f9435c3b519b6f234 --=20