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    SubjectRe: [PATCH v6 30/34] x86/mm, kexec: Allow kexec to be used with SME
    On Wed, Jun 07, 2017 at 02:18:27PM -0500, Tom Lendacky wrote:
    > Provide support so that kexec can be used to boot a kernel when SME is
    > enabled.
    >
    > Support is needed to allocate pages for kexec without encryption. This
    > is needed in order to be able to reboot in the kernel in the same manner
    > as originally booted.
    >
    > Additionally, when shutting down all of the CPUs we need to be sure to
    > flush the caches and then halt. This is needed when booting from a state
    > where SME was not active into a state where SME is active (or vice-versa).
    > Without these steps, it is possible for cache lines to exist for the same
    > physical location but tagged both with and without the encryption bit. This
    > can cause random memory corruption when caches are flushed depending on
    > which cacheline is written last.
    >
    > Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
    > ---
    > arch/x86/include/asm/init.h | 1 +
    > arch/x86/include/asm/kexec.h | 8 ++++++++
    > arch/x86/include/asm/pgtable_types.h | 1 +
    > arch/x86/kernel/machine_kexec_64.c | 35 +++++++++++++++++++++++++++++++++-
    > arch/x86/kernel/process.c | 17 +++++++++++++++--
    > arch/x86/mm/ident_map.c | 12 ++++++++----
    > include/linux/kexec.h | 14 ++++++++++++++
    > kernel/kexec_core.c | 6 ++++++
    > 8 files changed, 87 insertions(+), 7 deletions(-)
    >
    > diff --git a/arch/x86/include/asm/init.h b/arch/x86/include/asm/init.h
    > index 474eb8c..05c4aa0 100644
    > --- a/arch/x86/include/asm/init.h
    > +++ b/arch/x86/include/asm/init.h
    > @@ -7,6 +7,7 @@ struct x86_mapping_info {
    > unsigned long page_flag; /* page flag for PMD or PUD entry */
    > unsigned long offset; /* ident mapping offset */
    > bool direct_gbpages; /* PUD level 1GB page support */
    > + unsigned long kernpg_flag; /* kernel pagetable flag override */
    > };
    >
    > int kernel_ident_mapping_init(struct x86_mapping_info *info, pgd_t *pgd_page,
    > diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h
    > index 70ef205..e8183ac 100644
    > --- a/arch/x86/include/asm/kexec.h
    > +++ b/arch/x86/include/asm/kexec.h
    > @@ -207,6 +207,14 @@ struct kexec_entry64_regs {
    > uint64_t r15;
    > uint64_t rip;
    > };
    > +
    > +extern int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages,
    > + gfp_t gfp);
    > +#define arch_kexec_post_alloc_pages arch_kexec_post_alloc_pages
    > +
    > +extern void arch_kexec_pre_free_pages(void *vaddr, unsigned int pages);
    > +#define arch_kexec_pre_free_pages arch_kexec_pre_free_pages
    > +
    > #endif
    >
    > typedef void crash_vmclear_fn(void);
    > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
    > index ce8cb1c..0f326f4 100644
    > --- a/arch/x86/include/asm/pgtable_types.h
    > +++ b/arch/x86/include/asm/pgtable_types.h
    > @@ -213,6 +213,7 @@ enum page_cache_mode {
    > #define PAGE_KERNEL __pgprot(__PAGE_KERNEL | _PAGE_ENC)
    > #define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO | _PAGE_ENC)
    > #define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC | _PAGE_ENC)
    > +#define PAGE_KERNEL_EXEC_NOENC __pgprot(__PAGE_KERNEL_EXEC)
    > #define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX | _PAGE_ENC)
    > #define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE | _PAGE_ENC)
    > #define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE | _PAGE_ENC)
    > diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
    > index 6f5ca4e..35e069a 100644
    > --- a/arch/x86/kernel/machine_kexec_64.c
    > +++ b/arch/x86/kernel/machine_kexec_64.c
    > @@ -87,7 +87,7 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
    > set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE));
    > }
    > pte = pte_offset_kernel(pmd, vaddr);
    > - set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC));
    > + set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC_NOENC));
    > return 0;
    > err:
    > free_transition_pgtable(image);
    > @@ -115,6 +115,7 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
    > .alloc_pgt_page = alloc_pgt_page,
    > .context = image,
    > .page_flag = __PAGE_KERNEL_LARGE_EXEC,
    > + .kernpg_flag = _KERNPG_TABLE_NOENC,
    > };
    > unsigned long mstart, mend;
    > pgd_t *level4p;
    > @@ -602,3 +603,35 @@ void arch_kexec_unprotect_crashkres(void)
    > {
    > kexec_mark_crashkres(false);
    > }
    > +
    > +int arch_kexec_post_alloc_pages(void *vaddr, unsigned int pages, gfp_t gfp)
    > +{
    > + int ret;
    > +
    > + if (sme_active()) {

    What happened to flipping the logic and saving an indentation level here?

    > + /*
    > + * If SME is active we need to be sure that kexec pages are
    > + * not encrypted because when we boot to the new kernel the
    > + * pages won't be accessed encrypted (initially).
    > + */
    > + ret = set_memory_decrypted((unsigned long)vaddr, pages);
    > + if (ret)
    > + return ret;
    > +
    > + if (gfp & __GFP_ZERO)
    > + memset(vaddr, 0, pages * PAGE_SIZE);
    > + }

    This is still zeroing the memory a second time. That function has missed
    all my comments from last time.

    --
    Regards/Gruss,
    Boris.

    Good mailing practices for 400: avoid top-posting and trim the reply.

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