Messages in this thread Patch in this message | | | Date | Tue, 9 Apr 2019 10:40:31 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86: mm: Do not use set_{pud,pmd}_safe when splitting the large page |
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On Mon, Apr 08, 2019 at 07:11:21PM +0000, Singh, Brijesh wrote: > The following commit 0a9fe8ca844d ("x86/mm: Validate kernel_physical_mapping_init() > PTE population") triggers the below warning in the SEV guest. > > WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/pgalloc.h:87 phys_pmd_init+0x30d/0x386 > Call Trace: > kernel_physical_mapping_init+0xce/0x259 > early_set_memory_enc_dec+0x10f/0x160 > kvm_smp_prepare_boot_cpu+0x71/0x9d > start_kernel+0x1c9/0x50b > secondary_startup_64+0xa4/0xb0 > > The SEV guest calls kernel_physical_mapping_init() to clear the encryption > mask from an existing mapping. While clearing the encryption mask > kernel_physical_mapping_init() splits the large pages into the smaller. > To split the page, the kernel_physical_mapping_init() allocates a new page > and updates the existing entry. The set_{pud,pmd}_safe triggers warning > when updating the entry with page in the present state. We should use the > set_{pud,pmd} when updating an existing entry with the new entry. > > Updating an entry will also requires a TLB flush. Currently the caller > (early_set_memory_enc_dec()) is taking care of issuing the TLB flushes.
I'm not entirely sure I like this, this means all users of kernel_physical_mapping_init() now need to be aware and careful.
That said; the alternative is adding an argument to the function and propagating it through the callchain and dynamically switching between _safe and not. Which doesn't sound ideal either.
Anybody else got clever ideas?
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com> > Fixes: 0a9fe8ca844d (x86/mm: Validate kernel_physical_mapping_init() ...) > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Dave Hansen <dave.hansen@intel.com> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Cc: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Borislav Petkov <bp@alien8.de> > Cc: H. Peter Anvin <hpa@zytor.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Tom Lendacky <Thomas.Lendacky@amd.com> > --- > arch/x86/mm/init_64.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c > index bccff68e3267..0a26b64a99b9 100644 > --- a/arch/x86/mm/init_64.c > +++ b/arch/x86/mm/init_64.c > @@ -536,7 +536,7 @@ phys_pmd_init(pmd_t *pmd_page, unsigned long paddr, unsigned long paddr_end, > paddr_last = phys_pte_init(pte, paddr, paddr_end, new_prot); > > spin_lock(&init_mm.page_table_lock); > - pmd_populate_kernel_safe(&init_mm, pmd, pte); > + pmd_populate_kernel(&init_mm, pmd, pte); > spin_unlock(&init_mm.page_table_lock); > } > update_page_count(PG_LEVEL_2M, pages); > @@ -623,7 +623,7 @@ phys_pud_init(pud_t *pud_page, unsigned long paddr, unsigned long paddr_end, > page_size_mask, prot); > > spin_lock(&init_mm.page_table_lock); > - pud_populate_safe(&init_mm, pud, pmd); > + pud_populate(&init_mm, pud, pmd); > spin_unlock(&init_mm.page_table_lock); > } > > -- > 2.17.1 >
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