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 <brijesh.singh@xxxxxxx>
> Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx
> Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx>
> ---
> 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)
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