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Message-ID: <7185c055-fc9e-4510-a9bf-6245673f2f92@redhat.com>
Date: Wed, 23 Apr 2025 20:54:05 +0300
From: Mika Penttilä <mpenttil@...hat.com>
To: Leon Romanovsky <leon@...nel.org>,
Marek Szyprowski <m.szyprowski@...sung.com>, Jens Axboe <axboe@...nel.dk>,
Christoph Hellwig <hch@....de>, Keith Busch <kbusch@...nel.org>
Cc: Leon Romanovsky <leonro@...dia.com>, Jake Edge <jake@....net>,
Jonathan Corbet <corbet@....net>, Jason Gunthorpe <jgg@...pe.ca>,
Zhu Yanjun <zyjzyj2000@...il.com>, Robin Murphy <robin.murphy@....com>,
Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
Sagi Grimberg <sagi@...mberg.me>, Bjorn Helgaas <bhelgaas@...gle.com>,
Logan Gunthorpe <logang@...tatee.com>, Yishai Hadas <yishaih@...dia.com>,
Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
Kevin Tian <kevin.tian@...el.com>,
Alex Williamson <alex.williamson@...hat.com>,
Jérôme Glisse <jglisse@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
linux-rdma@...r.kernel.org, iommu@...ts.linux.dev,
linux-nvme@...ts.infradead.org, linux-pci@...r.kernel.org,
kvm@...r.kernel.org, linux-mm@...ck.org,
Niklas Schnelle <schnelle@...ux.ibm.com>,
Chuck Lever <chuck.lever@...cle.com>, Luis Chamberlain <mcgrof@...nel.org>,
Matthew Wilcox <willy@...radead.org>, Dan Williams
<dan.j.williams@...el.com>, Kanchan Joshi <joshi.k@...sung.com>,
Chaitanya Kulkarni <kch@...dia.com>
Subject: Re: [PATCH v9 10/24] mm/hmm: let users to tag specific PFN with DMA
mapped bit
Hi,
On 4/23/25 11:13, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
>
> Introduce new sticky flag (HMM_PFN_DMA_MAPPED), which isn't overwritten
> by HMM range fault. Such flag allows users to tag specific PFNs with
> information if this specific PFN was already DMA mapped.
>
> Tested-by: Jens Axboe <axboe@...nel.dk>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> ---
> include/linux/hmm.h | 17 +++++++++++++++
> mm/hmm.c | 51 ++++++++++++++++++++++++++++-----------------
> 2 files changed, 49 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 126a36571667..a1ddbedc19c0 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -23,6 +23,8 @@ struct mmu_interval_notifier;
> * HMM_PFN_WRITE - if the page memory can be written to (requires HMM_PFN_VALID)
> * HMM_PFN_ERROR - accessing the pfn is impossible and the device should
> * fail. ie poisoned memory, special pages, no vma, etc
> + * HMM_PFN_DMA_MAPPED - Flag preserved on input-to-output transformation
> + * to mark that page is already DMA mapped
> *
> * On input:
> * 0 - Return the current state of the page, do not fault it.
> @@ -36,6 +38,13 @@ enum hmm_pfn_flags {
> HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
> HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
> HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
> +
> + /*
> + * Sticky flags, carried from input to output,
> + * don't forget to update HMM_PFN_INOUT_FLAGS
> + */
> + HMM_PFN_DMA_MAPPED = 1UL << (BITS_PER_LONG - 7),
> +
How is this playing together with the mapped order usage?
> HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 8),
>
> /* Input flags */
> @@ -57,6 +66,14 @@ static inline struct page *hmm_pfn_to_page(unsigned long hmm_pfn)
> return pfn_to_page(hmm_pfn & ~HMM_PFN_FLAGS);
> }
>
> +/*
> + * hmm_pfn_to_phys() - return physical address pointed to by a device entry
> + */
> +static inline phys_addr_t hmm_pfn_to_phys(unsigned long hmm_pfn)
> +{
> + return __pfn_to_phys(hmm_pfn & ~HMM_PFN_FLAGS);
> +}
> +
> /*
> * hmm_pfn_to_map_order() - return the CPU mapping size order
> *
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 082f7b7c0b9e..51fe8b011cc7 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -39,13 +39,20 @@ enum {
> HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
> };
>
> +enum {
> + /* These flags are carried from input-to-output */
> + HMM_PFN_INOUT_FLAGS = HMM_PFN_DMA_MAPPED,
> +};
> +
> static int hmm_pfns_fill(unsigned long addr, unsigned long end,
> struct hmm_range *range, unsigned long cpu_flags)
> {
> unsigned long i = (addr - range->start) >> PAGE_SHIFT;
>
> - for (; addr < end; addr += PAGE_SIZE, i++)
> - range->hmm_pfns[i] = cpu_flags;
> + for (; addr < end; addr += PAGE_SIZE, i++) {
> + range->hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
> + range->hmm_pfns[i] |= cpu_flags;
> + }
> return 0;
> }
>
> @@ -202,8 +209,10 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
> return hmm_vma_fault(addr, end, required_fault, walk);
>
> pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
> - for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
> - hmm_pfns[i] = pfn | cpu_flags;
> + for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {
> + hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
> + hmm_pfns[i] |= pfn | cpu_flags;
> + }
> return 0;
> }
> #else /* CONFIG_TRANSPARENT_HUGEPAGE */
> @@ -230,14 +239,14 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
> unsigned long cpu_flags;
> pte_t pte = ptep_get(ptep);
> uint64_t pfn_req_flags = *hmm_pfn;
> + uint64_t new_pfn_flags = 0;
>
> if (pte_none_mostly(pte)) {
> required_fault =
> hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
> if (required_fault)
> goto fault;
> - *hmm_pfn = 0;
> - return 0;
> + goto out;
> }
>
> if (!pte_present(pte)) {
> @@ -253,16 +262,14 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
> cpu_flags = HMM_PFN_VALID;
> if (is_writable_device_private_entry(entry))
> cpu_flags |= HMM_PFN_WRITE;
> - *hmm_pfn = swp_offset_pfn(entry) | cpu_flags;
> - return 0;
> + new_pfn_flags = swp_offset_pfn(entry) | cpu_flags;
> + goto out;
> }
>
> required_fault =
> hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
> - if (!required_fault) {
> - *hmm_pfn = 0;
> - return 0;
> - }
> + if (!required_fault)
> + goto out;
>
> if (!non_swap_entry(entry))
> goto fault;
> @@ -304,11 +311,13 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
> pte_unmap(ptep);
> return -EFAULT;
> }
> - *hmm_pfn = HMM_PFN_ERROR;
> - return 0;
> + new_pfn_flags = HMM_PFN_ERROR;
> + goto out;
> }
>
> - *hmm_pfn = pte_pfn(pte) | cpu_flags;
> + new_pfn_flags = pte_pfn(pte) | cpu_flags;
> +out:
> + *hmm_pfn = (*hmm_pfn & HMM_PFN_INOUT_FLAGS) | new_pfn_flags;
> return 0;
>
> fault:
> @@ -448,8 +457,10 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
> }
>
> pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
> - for (i = 0; i < npages; ++i, ++pfn)
> - hmm_pfns[i] = pfn | cpu_flags;
> + for (i = 0; i < npages; ++i, ++pfn) {
> + hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
> + hmm_pfns[i] |= pfn | cpu_flags;
> + }
> goto out_unlock;
> }
>
> @@ -507,8 +518,10 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
> }
>
> pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);
> - for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
> - range->hmm_pfns[i] = pfn | cpu_flags;
> + for (; addr < end; addr += PAGE_SIZE, i++, pfn++) {
> + range->hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
> + range->hmm_pfns[i] |= pfn | cpu_flags;
> + }
>
> spin_unlock(ptl);
> return 0;
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