Re: [PATCH v3 5/6] fs/core/vmcore: Move sev_active() reference to x86 arch code

["Lendacky, Thomas" <Thomas.Lendacky@amd.com>]

On 7/17/19 10:28 PM, Thiago Jung Bauermann wrote:
> Secure Encrypted Virtualization is an x86-specific feature, so it shouldn't
> appear in generic kernel code because it forces non-x86 architectures to
> define the sev_active() function, which doesn't make a lot of sense.
> 
> To solve this problem, add an x86 elfcorehdr_read() function to override
> the generic weak implementation. To do that, it's necessary to make
> read_from_oldmem() public so that it can be used outside of vmcore.c.
> 
> Also, remove the export for sev_active() since it's only used in files that
> won't be built as modules.
> 
> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>

Adding Lianbo and Baoquan, who recently worked on this, for their review.

Thanks,
Tom

> ---
>  arch/x86/kernel/crash_dump_64.c |  5 +++++
>  arch/x86/mm/mem_encrypt.c       |  1 -
>  fs/proc/vmcore.c                |  8 ++++----
>  include/linux/crash_dump.h      | 14 ++++++++++++++
>  include/linux/mem_encrypt.h     |  1 -
>  5 files changed, 23 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash_dump_64.c b/arch/x86/kernel/crash_dump_64.c
> index 22369dd5de3b..045e82e8945b 100644
> --- a/arch/x86/kernel/crash_dump_64.c
> +++ b/arch/x86/kernel/crash_dump_64.c
> @@ -70,3 +70,8 @@ ssize_t copy_oldmem_page_encrypted(unsigned long pfn, char *buf, size_t csize,
>  {
>  	return __copy_oldmem_page(pfn, buf, csize, offset, userbuf, true);
>  }
> +
> +ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos)
> +{
> +	return read_from_oldmem(buf, count, ppos, 0, sev_active());
> +}
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 7139f2f43955..b1e823441093 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -349,7 +349,6 @@ bool sev_active(void)
>  {
>  	return sme_me_mask && sev_enabled;
>  }
> -EXPORT_SYMBOL(sev_active);
>  
>  /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
>  bool force_dma_unencrypted(struct device *dev)
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index 57957c91c6df..ca1f20bedd8c 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -100,9 +100,9 @@ static int pfn_is_ram(unsigned long pfn)
>  }
>  
>  /* Reads a page from the oldmem device from given offset. */
> -static ssize_t read_from_oldmem(char *buf, size_t count,
> -				u64 *ppos, int userbuf,
> -				bool encrypted)
> +ssize_t read_from_oldmem(char *buf, size_t count,
> +			 u64 *ppos, int userbuf,
> +			 bool encrypted)
>  {
>  	unsigned long pfn, offset;
>  	size_t nr_bytes;
> @@ -166,7 +166,7 @@ void __weak elfcorehdr_free(unsigned long long addr)
>   */
>  ssize_t __weak elfcorehdr_read(char *buf, size_t count, u64 *ppos)
>  {
> -	return read_from_oldmem(buf, count, ppos, 0, sev_active());
> +	return read_from_oldmem(buf, count, ppos, 0, false);
>  }
>  
>  /*
> diff --git a/include/linux/crash_dump.h b/include/linux/crash_dump.h
> index f774c5eb9e3c..4664fc1871de 100644
> --- a/include/linux/crash_dump.h
> +++ b/include/linux/crash_dump.h
> @@ -115,4 +115,18 @@ static inline int vmcore_add_device_dump(struct vmcoredd_data *data)
>  	return -EOPNOTSUPP;
>  }
>  #endif /* CONFIG_PROC_VMCORE_DEVICE_DUMP */
> +
> +#ifdef CONFIG_PROC_VMCORE
> +ssize_t read_from_oldmem(char *buf, size_t count,
> +			 u64 *ppos, int userbuf,
> +			 bool encrypted);
> +#else
> +static inline ssize_t read_from_oldmem(char *buf, size_t count,
> +				       u64 *ppos, int userbuf,
> +				       bool encrypted)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#endif /* CONFIG_PROC_VMCORE */
> +
>  #endif /* LINUX_CRASHDUMP_H */
> diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
> index 0c5b0ff9eb29..5c4a18a91f89 100644
> --- a/include/linux/mem_encrypt.h
> +++ b/include/linux/mem_encrypt.h
> @@ -19,7 +19,6 @@
>  #else	/* !CONFIG_ARCH_HAS_MEM_ENCRYPT */
>  
>  static inline bool mem_encrypt_active(void) { return false; }
> -static inline bool sev_active(void) { return false; }
>  
>  #endif	/* CONFIG_ARCH_HAS_MEM_ENCRYPT */
>  
>