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SubjectRe: [PATCH 3/3] fs/core/vmcore: Move sev_active() reference to x86 arch code
On Fri, 12 Jul 2019 02:36:31 -0300
Thiago Jung Bauermann <bauerman@linux.ibm.com> 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.

sev_active() might be just bad (too specific) name for a general
concept. s390 code defines it drives the right behavior in
kernel/dma/direct.c (which uses it).

>
> 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.
>
> Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
> ---
> arch/x86/kernel/crash_dump_64.c | 5 +++++
> fs/proc/vmcore.c | 8 ++++----
> include/linux/crash_dump.h | 14 ++++++++++++++
> include/linux/mem_encrypt.h | 1 -
> 4 files changed, 23 insertions(+), 5 deletions(-)

Does not seem to apply to today's or yesterdays master.

>
> 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/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 f2e399fb626b..a3747fcae466 100644
> --- a/include/linux/mem_encrypt.h
> +++ b/include/linux/mem_encrypt.h
> @@ -21,7 +21,6 @@
>
> #else /* !CONFIG_ARCH_HAS_MEM_ENCRYPT */
>
> -static inline bool sev_active(void) { return false; }

This is the implementation for the guys that don't
have ARCH_HAS_MEM_ENCRYPT.

Means sev_active() may not be used in such code after this
patch. What about

static inline bool force_dma_unencrypted(void)
{
return sev_active();
}

in kernel/dma/direct.c?

Regards,
Halil

> static inline bool mem_encrypt_active(void) { return false; }
>
> #endif /* CONFIG_ARCH_HAS_MEM_ENCRYPT */

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