On Fri, Sep 07, 2018 at 12:57:30PM -0500, Brijesh Singh wrote:
> Currently, the per-cpu pvclock data is allocated dynamically when
> cpu > HVC_BOOT_ARRAY_SIZE.
Well no, you need to write this correctly - what is "cpu >
HVC_BOOT_ARRAY_SIZE" ?!
( I know what it is but I know it only because I've looked at that code before. )
So no, please explain it in English not in code.
> 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.
This sentence is a good example about how to explain stuff in commit
messages.
> The C-bit works on a page,
"The C-bit determines the encryption status of a 4K page."
> hence we will be required to perform a
Use passive tone in your commit message: no "we", etc...
> full 4k page allocation to store a single 32-byte pvclock variable. It
> will waste fairly sizeable amount of memory since each CPU will be doing
"... will waste *a* fairly sizeable amount of ..."
> a separate 4k allocation.
Start new paragraph here and use passive tone.
> Let's define a second array for the SEV case to
> statically allocate for NR_CPUS and put this array in .data..decrypted
NR_CPUS needs explaining for the unenlightened reader. Also,
"... put this array in *the* .data..decrypted section... "
> section so that its mapped with C=0 during boot.
<---- newline here.
> The .data..decrypted
> section has a big chunk of memory that is currently unused. And since
> second array will be used only when memory encryption is active hence
"... since *the* second array... "
s/hence //
> free it when encryption is not active.
>
> 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 | 14 ++++++++++++++
> arch/x86/kernel/vmlinux.lds.S | 3 +++
> arch/x86/mm/init.c | 3 +++
> arch/x86/mm/mem_encrypt.c | 10 ++++++++++
> 5 files changed, 34 insertions(+)
>
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 802b2eb..cc46584 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);
Proper prefixing:
"mem_encrypt_free_decrypted"
or so
> bool sme_active(void);
> bool sev_active(void);
>
> #define __decrypted __attribute__((__section__(".data..decrypted")))
> +#define __decrypted_aux __attribute__((__section__(".data..decrypted.aux")))
>
> #else /* !CONFIG_AMD_MEM_ENCRYPT */
>
> @@ -80,6 +82,7 @@ static inline int __init
> early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0; }
>
> #define __decrypted
> +#define __decrypted_aux
>
> #endif /* CONFIG_AMD_MEM_ENCRYPT */
>
> @@ -93,6 +96,7 @@ early_set_memory_encrypted(unsigned long vaddr, unsigned long size) { return 0;
> #define __sme_pa_nodebug(x) (__pa_nodebug(x) | sme_me_mask)
>
> extern char __start_data_decrypted[], __end_data_decrypted[];
> +extern char __start_data_decrypted_aux[];
>
> #endif /* __ASSEMBLY__ */
>
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index 376fd3a..6086b56 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -65,6 +65,15 @@ static struct pvclock_vsyscall_time_info
> static struct pvclock_wall_clock wall_clock __decrypted;
> static DEFINE_PER_CPU(struct pvclock_vsyscall_time_info *, hv_clock_per_cpu);
>
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +/*
> + * The auxiliary array will be used when SEV is active. In non-SEV case,
> + * it will be freed by free_decrypted_mem().
> + */
> +static struct pvclock_vsyscall_time_info
> + hv_clock_aux[NR_CPUS] __decrypted_aux;
Hmm, so worst case that's 64 4K pages:
(8192*32)/4096 = 64 4K pages.
Now, the real question from all this SNAFU is, why can't all those point
to a single struct pvclock_vsyscall_time_info and all CPUs read a single
thing? Why do they have to be per-CPU and thus waste so much memory?
--
Regards/Gruss,
Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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