From mboxrd@z Thu Jan 1 00:00:00 1970 From: Borislav Petkov Subject: Re: [PATCH v5 5/5] x86/kvm: Avoid dynamic allocation of pvclock data when SEV is active Date: Thu, 6 Sep 2018 14:24:23 +0200 Message-ID: <20180906122423.GA11144@zn.tnic> References: <1536234182-2809-1-git-send-email-brijesh.singh@amd.com> <1536234182-2809-6-git-send-email-brijesh.singh@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: x86@kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Tom Lendacky , Thomas Gleixner , "H. Peter Anvin" , Paolo Bonzini , Sean Christopherson , Radim =?utf-8?B?S3LEjW3DocWZ?= To: Brijesh Singh Return-path: Content-Disposition: inline In-Reply-To: <1536234182-2809-6-git-send-email-brijesh.singh@amd.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, Sep 06, 2018 at 06:43:02AM -0500, Brijesh Singh wrote: > Currently, the per-cpu pvclock data is allocated dynamically when > cpu > HVC_BOOT_ARRAY_SIZE. The physical address of this variable is > shared between the guest and the hypervisor hence it must be mapped as > unencrypted (ie. C=0) when SEV is active. > > When SEV is active, we will be wasting fairly sizeable amount of memory > since each CPU will be doing a separate 4k allocation so that it can clear > C-bit. Let's define few extra static page sized array of pvclock data. > In the preparatory stage of CPU hotplug, use the element of this static > array to avoid the dynamic allocation. This array will be put in > the .data..decrypted section so that its mapped with C=0 during the boot. > > In non-SEV case, this static page will unused and free'd by the > free_decrypted_mem(). > > Signed-off-by: Brijesh Singh > Suggested-by: Sean Christopherson > Cc: Tom Lendacky > Cc: kvm@vger.kernel.org > Cc: Thomas Gleixner > Cc: Borislav Petkov > Cc: "H. Peter Anvin" > Cc: linux-kernel@vger.kernel.org > Cc: Paolo Bonzini > Cc: Sean Christopherson > Cc: kvm@vger.kernel.org > Cc: "Radim Krčmář" > --- > arch/x86/include/asm/mem_encrypt.h | 4 ++++ > arch/x86/kernel/kvmclock.c | 22 +++++++++++++++++++--- > arch/x86/kernel/vmlinux.lds.S | 3 +++ > arch/x86/mm/init.c | 3 +++ > arch/x86/mm/mem_encrypt.c | 10 ++++++++++ > 5 files changed, 39 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h > index 802b2eb..aa204af 100644 > --- a/arch/x86/include/asm/mem_encrypt.h > +++ b/arch/x86/include/asm/mem_encrypt.h > @@ -48,11 +48,13 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size); > > /* Architecture __weak replacement functions */ > void __init mem_encrypt_init(void); > +void __init free_decrypted_mem(void); > > bool sme_active(void); > bool sev_active(void); > > #define __decrypted __attribute__((__section__(".data..decrypted"))) > +#define __decrypted_hvclock __attribute__((__section__(".data..decrypted_hvclock"))) So are we going to be defining a decrypted section for every piece of machinery now? That's a bit too much in my book. Why can't you simply free everything in .data..decrypted on !SVE guests? -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --