| Message ID | 20240523223745.395337-3-peterx@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/x86/pat: Fix two possible issues | expand |
On 5/23/24 15:37, Peter Xu wrote: > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 317de2afd371..c4a2356b1a54 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -1135,7 +1135,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > goto out_unlock; > } > > - entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); > + entry = pmd_mkhuge(pfn_t_pmd(pfn, pgprot_4k_2_large(prot))); > if (pfn_t_devmap(pfn)) > entry = pmd_mkdevmap(entry); > if (write) { Does this even compile on non-x86 architectures?
On Thu, May 23, 2024 at 03:48:22PM -0700, Dave Hansen wrote: > On 5/23/24 15:37, Peter Xu wrote: > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 317de2afd371..c4a2356b1a54 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -1135,7 +1135,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > > goto out_unlock; > > } > > > > - entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); > > + entry = pmd_mkhuge(pfn_t_pmd(pfn, pgprot_4k_2_large(prot))); > > if (pfn_t_devmap(pfn)) > > entry = pmd_mkdevmap(entry); > > if (write) { > > Does this even compile on non-x86 architectures? Probably not.. I think I can define a pgprot_to_large() globally, pointing that to pgprot_4k_2_large() on x86 and make the fallback to be noop. And if there's a new version I'll guarantee to run over my cross compilers. Any comments on the idea itself? Do we have a problem, or maybe I overlooked something? Thanks,
On Thu, May 23, 2024 at 07:07:06PM -0400, Peter Xu wrote: > On Thu, May 23, 2024 at 03:48:22PM -0700, Dave Hansen wrote: > > On 5/23/24 15:37, Peter Xu wrote: > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > > index 317de2afd371..c4a2356b1a54 100644 > > > --- a/mm/huge_memory.c > > > +++ b/mm/huge_memory.c > > > @@ -1135,7 +1135,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, > > > goto out_unlock; > > > } > > > > > > - entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); > > > + entry = pmd_mkhuge(pfn_t_pmd(pfn, pgprot_4k_2_large(prot))); > > > if (pfn_t_devmap(pfn)) > > > entry = pmd_mkdevmap(entry); > > > if (write) { > > > > Does this even compile on non-x86 architectures? > > Probably not.. I think I can define a pgprot_to_large() globally, pointing > that to pgprot_4k_2_large() on x86 and make the fallback to be noop. And > if there's a new version I'll guarantee to run over my cross compilers. > > Any comments on the idea itself? Do we have a problem, or maybe I > overlooked something? I also attached one new version of patch 2 that should pass the cross builds. Please reviewers feel free to look at this one instead. From x86 perspective they should be the same thing. Thanks, ===8<=== From 1cce12c872cb01aaa8686d8f5c7cd6b266ca4e38 Mon Sep 17 00:00:00 2001 From: Peter Xu <peterx@redhat.com> Date: Thu, 23 May 2024 18:19:35 -0400 Subject: [PATCH rfcv1.1] mm/x86/pat: Do proper PAT bit shift for large mappings For large mappings, the pgtable PAT is set on bit 12 (_PAGE_PAT_LARGE) rather than bit 9 (_PAGE_PAT), while bit 9 is used as PAE hint. Do proper shifting when inject large pfn pgtable mappings to make cache mode alright. Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: x86@kernel.org Signed-off-by: Peter Xu <peterx@redhat.com> --- arch/x86/include/asm/pgtable_types.h | 1 + include/linux/pgtable.h | 4 ++++ mm/huge_memory.c | 4 ++-- 3 files changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h index b78644962626..f9edb2bb1512 100644 --- a/arch/x86/include/asm/pgtable_types.h +++ b/arch/x86/include/asm/pgtable_types.h @@ -512,6 +512,7 @@ static inline pgprot_t pgprot_large_2_4k(pgprot_t pgprot) return __pgprot(protval_large_2_4k(pgprot_val(pgprot))); } +#define pgprot_to_large(pgprot) pgprot_4k_2_large(pgprot) typedef struct page *pgtable_t; diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 18019f037bae..54487d2b3e40 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -1956,4 +1956,8 @@ pgprot_t vm_get_page_prot(unsigned long vm_flags) \ } \ EXPORT_SYMBOL(vm_get_page_prot); +#ifndef pgprot_to_large +#define pgprot_to_large(pgprot) pgprot +#endif + #endif /* _LINUX_PGTABLE_H */ diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 317de2afd371..4c134a60fb64 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1135,7 +1135,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, goto out_unlock; } - entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); + entry = pmd_mkhuge(pfn_t_pmd(pfn, pgprot_to_large(prot))); if (pfn_t_devmap(pfn)) entry = pmd_mkdevmap(entry); if (write) { @@ -1233,7 +1233,7 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr, goto out_unlock; } - entry = pud_mkhuge(pfn_t_pud(pfn, prot)); + entry = pud_mkhuge(pfn_t_pud(pfn, pgprot_to_large(prot))); if (pfn_t_devmap(pfn)) entry = pud_mkdevmap(entry); if (write) {
On 5/23/24 16:07, Peter Xu wrote: > Probably not.. I think I can define a pgprot_to_large() globally, pointing > that to pgprot_4k_2_large() on x86 and make the fallback to be noop. And > if there's a new version I'll guarantee to run over my cross compilers. I guess that would be functional, but it would be a bit mean to everybody else. > Any comments on the idea itself? Do we have a problem, or maybe I > overlooked something? I think it's probably unnecessary to inflict this particular x86-ism on generic code. The arch-generic 'prot' should have PAT at its 4k (_PAGE_BIT_PAT) position and then p*d_mkhuge() can shift it into the _PAGE_BIT_PAT_LARGE spot.
On Thu, May 23, 2024 at 08:30:19PM -0700, Dave Hansen wrote: > On 5/23/24 16:07, Peter Xu wrote: > > Probably not.. I think I can define a pgprot_to_large() globally, pointing > > that to pgprot_4k_2_large() on x86 and make the fallback to be noop. And > > if there's a new version I'll guarantee to run over my cross compilers. > > I guess that would be functional, but it would be a bit mean to > everybody else. > > > Any comments on the idea itself? Do we have a problem, or maybe I > > overlooked something? > > I think it's probably unnecessary to inflict this particular x86-ism on > generic code. The arch-generic 'prot' should have PAT at its 4k > (_PAGE_BIT_PAT) position and then p*d_mkhuge() can shift it into the > _PAGE_BIT_PAT_LARGE spot. Right that's another option indeed. It's just that I found it might in many cases be better when we have the API separately properly and making the pairs matching each other. For example, it could be clearer if pxx_mkhuge() does exactly what pxx_leaf() would check against. PS: I hoped it's called pxx_huge() already to make the name paired with each other; afaict we called it pxx_leaf() only because pxx_huge() used to be "abused" by hugetlbfs before.. now it's gone. The other thing is we mostly only need these knobs for special maps like pfnmaps, am I right? OTOH we use WB for RAMs, and maybe we don't want to bother any PAT stuff when the kernel is installing a THP anonymous? IMHO having pgprot_to_large() is fine even if only x86 has it; it's really like pfn tracking itself which is noop for !x86. but I'll follow your advise if you still insist; I don't really have a strong opinion. But if so I'd also like to mention a 3rd option, which is to have pxx_mkhuge_prot(), fallback to pxx_mkhuge() for !x86. That'll make pxx_huge() untainted for x86. I'm not sure whether that would ease the same concern, though. In all cases, thanks for confirming this issue, I appreciate that. Let me know if you have any comment on patch 1 too; that one isn't a problem so far iiuc, but it can be soon. Thanks,
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 317de2afd371..c4a2356b1a54 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1135,7 +1135,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr, goto out_unlock; } - entry = pmd_mkhuge(pfn_t_pmd(pfn, prot)); + entry = pmd_mkhuge(pfn_t_pmd(pfn, pgprot_4k_2_large(prot))); if (pfn_t_devmap(pfn)) entry = pmd_mkdevmap(entry); if (write) { @@ -1233,7 +1233,7 @@ static void insert_pfn_pud(struct vm_area_struct *vma, unsigned long addr, goto out_unlock; } - entry = pud_mkhuge(pfn_t_pud(pfn, prot)); + entry = pud_mkhuge(pfn_t_pud(pfn, pgprot_4k_2_large(prot))); if (pfn_t_devmap(pfn)) entry = pud_mkdevmap(entry); if (write) {
For large mappings, the pgtable PAT is set on bit 12 (_PAGE_PAT_LARGE) rather than bit 9 (_PAGE_PAT), while bit 9 is used as PAE hint. Do proper shifting when inject large pfn pgtable mappings to make cache mode alright. Cc: Alex Williamson <alex.williamson@redhat.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Kirill A. Shutemov <kirill@shutemov.name> Cc: x86@kernel.org Signed-off-by: Peter Xu <peterx@redhat.com> --- mm/huge_memory.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)