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From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien@xen.org>
Cc: xen-devel@lists.xenproject.org,
	Julien Grall <julien.grall@arm.com>,
	 Stefano Stabellini <sstabellini@kernel.org>,
	 Bertrand Marquis <bertrand.marquis@arm.com>,
	 Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	 Julien Grall <jgrall@amazon.com>,
	Hongda Deng <Hongda.Heng@arm.com>
Subject: Re: [PATCH 01/16] xen/arm: mm: Allow other mapping size in xen_pt_update_entry()
Date: Fri, 3 Jun 2022 15:27:34 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.22.394.2206031526280.2783803@ubuntu-linux-20-04-desktop> (raw)
In-Reply-To: <20220520120937.28925-2-julien@xen.org>

On Fri, 20 May 2022, Julien Grall wrote:
> From: Julien Grall <julien.grall@arm.com>
> 
> At the moment, xen_pt_update_entry() only supports mapping at level 3
> (i.e 4KB mapping). While this is fine for most of the runtime helper,
> the boot code will require to use superpage mapping.
> 
> We don't want to allow superpage mapping by default as some of the
> callers may expect small mappings (i.e populate_pt_range()) or even
> expect to unmap only a part of a superpage.
> 
> To keep the code simple, a new flag _PAGE_BLOCK is introduced to
> allow the caller to enable superpage mapping.
> 
> As the code doesn't support all the combinations, xen_pt_check_entry()
> is extended to take into account the cases we don't support when
> using block mapping:
>     - Replacing a table with a mapping. This may happen if region was
>     first mapped with 4KB mapping and then later on replaced with a 2MB
>     (or 1GB mapping).
>     - Removing/modifying a table. This may happen if a caller try to
>     remove a region with _PAGE_BLOCK set when it was created without it.
> 
> Note that the current restriction means that the caller must ensure that
> _PAGE_BLOCK is consistently set/cleared across all the updates on a
> given virtual region. This ought to be fine with the expected use-cases.
> 
> More rework will be necessary if we wanted to remove the restrictions.
> 
> Note that nr_mfns is now marked const as it is used for flushing the
> TLBs and we don't want it to be modified.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>
> Signed-off-by: Julien Grall <jgrall@amazon.com>
> Reviewed-by: Hongda Deng <Hongda.Heng@arm.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
>     Changes in v4:
>         - Add Hongda's reviewed-by
>         - Add a comment why nr_mfns is const
>         - Open-code pfn_to_paddr()
> 
>     Changes in v3:
>         - Fix clash after prefixing the PT macros with XEN_PT_
>         - Fix typoes in the commit message
>         - Support superpage mappings even if nr is not suitably aligned
>         - Move the logic to find the level in a separate function
> 
>     Changes in v2:
>         - Pass the target level rather than the order to
>         xen_pt_update_entry()
>         - Update some comments
>         - Open-code paddr_to_pfn()
>         - Add my AWS signed-off-by
> ---
>  xen/arch/arm/include/asm/page.h |   4 ++
>  xen/arch/arm/mm.c               | 109 ++++++++++++++++++++++++++------
>  2 files changed, 95 insertions(+), 18 deletions(-)
> 
> diff --git a/xen/arch/arm/include/asm/page.h b/xen/arch/arm/include/asm/page.h
> index c6f9fb0d4e0c..07998df47bac 100644
> --- a/xen/arch/arm/include/asm/page.h
> +++ b/xen/arch/arm/include/asm/page.h
> @@ -69,6 +69,7 @@
>   * [3:4] Permission flags
>   * [5]   Page present
>   * [6]   Only populate page tables
> + * [7]   Superpage mappings is allowed
>   */
>  #define PAGE_AI_MASK(x) ((x) & 0x7U)
>  
> @@ -82,6 +83,9 @@
>  #define _PAGE_PRESENT    (1U << 5)
>  #define _PAGE_POPULATE   (1U << 6)
>  
> +#define _PAGE_BLOCK_BIT     7
> +#define _PAGE_BLOCK         (1U << _PAGE_BLOCK_BIT)
> +
>  /*
>   * _PAGE_DEVICE and _PAGE_NORMAL are convenience defines. They are not
>   * meant to be used outside of this header.
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 7b1f2f49060d..be2ac302d731 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -1078,9 +1078,10 @@ static int xen_pt_next_level(bool read_only, unsigned int level,
>  }
>  
>  /* Sanity check of the entry */
> -static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int flags)
> +static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int level,
> +                               unsigned int flags)
>  {
> -    /* Sanity check when modifying a page. */
> +    /* Sanity check when modifying an entry. */
>      if ( (flags & _PAGE_PRESENT) && mfn_eq(mfn, INVALID_MFN) )
>      {
>          /* We don't allow modifying an invalid entry. */
> @@ -1090,6 +1091,13 @@ static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int flags)
>              return false;
>          }
>  
> +        /* We don't allow modifying a table entry */
> +        if ( !lpae_is_mapping(entry, level) )
> +        {
> +            mm_printk("Modifying a table entry is not allowed.\n");
> +            return false;
> +        }
> +
>          /* We don't allow changing memory attributes. */
>          if ( entry.pt.ai != PAGE_AI_MASK(flags) )
>          {
> @@ -1105,7 +1113,7 @@ static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int flags)
>              return false;
>          }
>      }
> -    /* Sanity check when inserting a page */
> +    /* Sanity check when inserting a mapping */
>      else if ( flags & _PAGE_PRESENT )
>      {
>          /* We should be here with a valid MFN. */
> @@ -1114,18 +1122,28 @@ static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int flags)
>          /* We don't allow replacing any valid entry. */
>          if ( lpae_is_valid(entry) )
>          {
> -            mm_printk("Changing MFN for a valid entry is not allowed (%#"PRI_mfn" -> %#"PRI_mfn").\n",
> -                      mfn_x(lpae_get_mfn(entry)), mfn_x(mfn));
> +            if ( lpae_is_mapping(entry, level) )
> +                mm_printk("Changing MFN for a valid entry is not allowed (%#"PRI_mfn" -> %#"PRI_mfn").\n",
> +                          mfn_x(lpae_get_mfn(entry)), mfn_x(mfn));
> +            else
> +                mm_printk("Trying to replace a table with a mapping.\n");
>              return false;
>          }
>      }
> -    /* Sanity check when removing a page. */
> +    /* Sanity check when removing a mapping. */
>      else if ( (flags & (_PAGE_PRESENT|_PAGE_POPULATE)) == 0 )
>      {
>          /* We should be here with an invalid MFN. */
>          ASSERT(mfn_eq(mfn, INVALID_MFN));
>  
> -        /* We don't allow removing page with contiguous bit set. */
> +        /* We don't allow removing a table */
> +        if ( lpae_is_table(entry, level) )
> +        {
> +            mm_printk("Removing a table is not allowed.\n");
> +            return false;
> +        }
> +
> +        /* We don't allow removing a mapping with contiguous bit set. */
>          if ( entry.pt.contig )
>          {
>              mm_printk("Removing entry with contiguous bit set is not allowed.\n");
> @@ -1143,13 +1161,13 @@ static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int flags)
>      return true;
>  }
>  
> +/* Update an entry at the level @target. */
>  static int xen_pt_update_entry(mfn_t root, unsigned long virt,
> -                               mfn_t mfn, unsigned int flags)
> +                               mfn_t mfn, unsigned int target,
> +                               unsigned int flags)
>  {
>      int rc;
>      unsigned int level;
> -    /* We only support 4KB mapping (i.e level 3) for now */
> -    unsigned int target = 3;
>      lpae_t *table;
>      /*
>       * The intermediate page tables are read-only when the MFN is not valid
> @@ -1204,7 +1222,7 @@ static int xen_pt_update_entry(mfn_t root, unsigned long virt,
>      entry = table + offsets[level];
>  
>      rc = -EINVAL;
> -    if ( !xen_pt_check_entry(*entry, mfn, flags) )
> +    if ( !xen_pt_check_entry(*entry, mfn, level, flags) )
>          goto out;
>  
>      /* If we are only populating page-table, then we are done. */
> @@ -1222,8 +1240,11 @@ static int xen_pt_update_entry(mfn_t root, unsigned long virt,
>          {
>              pte = mfn_to_xen_entry(mfn, PAGE_AI_MASK(flags));
>  
> -            /* Third level entries set pte.pt.table = 1 */
> -            pte.pt.table = 1;
> +            /*
> +             * First and second level pages set pte.pt.table = 0, but
> +             * third level entries set pte.pt.table = 1.
> +             */
> +            pte.pt.table = (level == 3);
>          }
>          else /* We are updating the permission => Copy the current pte. */
>              pte = *entry;
> @@ -1243,15 +1264,57 @@ out:
>      return rc;
>  }
>  
> +/* Return the level where mapping should be done */
> +static int xen_pt_mapping_level(unsigned long vfn, mfn_t mfn, unsigned long nr,
> +                                unsigned int flags)
> +{
> +    unsigned int level;
> +    unsigned long mask;
> +
> +    /*
> +      * Don't take into account the MFN when removing mapping (i.e
> +      * MFN_INVALID) to calculate the correct target order.
> +      *
> +      * Per the Arm Arm, `vfn` and `mfn` must be both superpage aligned.
> +      * They are or-ed together and then checked against the size of
> +      * each level.
> +      *
> +      * `left` is not included and checked separately to allow
> +      * superpage mapping even if it is not properly aligned (the
> +      * user may have asked to map 2MB + 4k).
> +      */
> +     mask = !mfn_eq(mfn, INVALID_MFN) ? mfn_x(mfn) : 0;
> +     mask |= vfn;
> +
> +     /*
> +      * Always use level 3 mapping unless the caller request block
> +      * mapping.
> +      */
> +     if ( likely(!(flags & _PAGE_BLOCK)) )
> +         level = 3;
> +     else if ( !(mask & (BIT(FIRST_ORDER, UL) - 1)) &&
> +               (nr >= BIT(FIRST_ORDER, UL)) )
> +         level = 1;
> +     else if ( !(mask & (BIT(SECOND_ORDER, UL) - 1)) &&
> +               (nr >= BIT(SECOND_ORDER, UL)) )
> +         level = 2;
> +     else
> +         level = 3;
> +
> +     return level;
> +}
> +
>  static DEFINE_SPINLOCK(xen_pt_lock);
>  
>  static int xen_pt_update(unsigned long virt,
>                           mfn_t mfn,
> -                         unsigned long nr_mfns,
> +                         /* const on purpose as it is used for TLB flush */
> +                         const unsigned long nr_mfns,
>                           unsigned int flags)
>  {
>      int rc = 0;
> -    unsigned long addr = virt, addr_end = addr + nr_mfns * PAGE_SIZE;
> +    unsigned long vfn = virt >> PAGE_SHIFT;
> +    unsigned long left = nr_mfns;
>  
>      /*
>       * For arm32, page-tables are different on each CPUs. Yet, they share
> @@ -1283,14 +1346,24 @@ static int xen_pt_update(unsigned long virt,
>  
>      spin_lock(&xen_pt_lock);
>  
> -    for ( ; addr < addr_end; addr += PAGE_SIZE )
> +    while ( left )
>      {
> -        rc = xen_pt_update_entry(root, addr, mfn, flags);
> +        unsigned int order, level;
> +
> +        level = xen_pt_mapping_level(vfn, mfn, left, flags);
> +        order = XEN_PT_LEVEL_ORDER(level);
> +
> +        ASSERT(left >= BIT(order, UL));
> +
> +        rc = xen_pt_update_entry(root, vfn << PAGE_SHIFT, mfn, level, flags);
>          if ( rc )
>              break;
>  
> +        vfn += 1U << order;
>          if ( !mfn_eq(mfn, INVALID_MFN) )
> -            mfn = mfn_add(mfn, 1);
> +            mfn = mfn_add(mfn, 1U << order);
> +
> +        left -= (1U << order);
>      }
>  
>      /*
> -- 
> 2.32.0
> 


  reply	other threads:[~2022-06-03 22:28 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-20 12:09 [PATCH 00/16] xen/arm: mm: Remove open-coding mappings Julien Grall
2022-05-20 12:09 ` [PATCH 01/16] xen/arm: mm: Allow other mapping size in xen_pt_update_entry() Julien Grall
2022-06-03 22:27   ` Stefano Stabellini [this message]
2022-05-20 12:09 ` [PATCH 02/16] xen/arm: mm: Add support for the contiguous bit Julien Grall
2022-05-20 12:09 ` [PATCH 03/16] xen/arm: mm: Avoid flushing the TLBs when mapping are inserted Julien Grall
2022-05-26 15:28   ` Luca Fancellu
2022-06-03 22:30   ` Stefano Stabellini
2022-05-20 12:09 ` [PATCH 04/16] xen/arm: mm: Don't open-code Xen PT update in remove_early_mappings() Julien Grall
2022-06-03 22:31   ` Stefano Stabellini
2022-05-20 12:09 ` [PATCH 05/16] xen/arm: mm: Re-implement early_fdt_map() using map_pages_to_xen() Julien Grall
2022-06-03 22:33   ` Stefano Stabellini
2022-05-20 12:09 ` [PATCH 06/16] xen/arm32: mm: Re-implement setup_xenheap_mappings() " Julien Grall
2022-05-20 12:09 ` [PATCH 07/16] xen/arm: mm: Allocate xen page tables in domheap rather than xenheap Julien Grall
2022-05-20 12:09 ` [PATCH 08/16] xen/arm: mm: Allow page-table allocation from the boot allocator Julien Grall
2022-05-20 12:09 ` [PATCH 09/16] xen/arm: Move fixmap definitions in a separate header Julien Grall
2022-06-08  1:08   ` Stefano Stabellini
2022-05-20 12:09 ` [PATCH 10/16] xen/arm: add Persistent Map (PMAP) infrastructure Julien Grall
2022-05-21 11:38   ` Julien Grall
2022-05-24  2:11   ` Wei Chen
2022-05-24  8:58     ` Julien Grall
2022-05-26 15:55   ` Luca Fancellu
2022-06-08  1:08   ` Stefano Stabellini
2022-06-08 10:01     ` Julien Grall
2022-06-09  0:25       ` Stefano Stabellini
2022-05-20 12:09 ` [PATCH 11/16] xen/arm: mm: Clean-up the includes and order them Julien Grall
2022-05-20 12:09 ` [PATCH 12/16] xen/arm: mm: Use the PMAP helpers in xen_{,un}map_table() Julien Grall
2022-05-20 12:09 ` [PATCH 13/16] xen/arm32: setup: Move out the code to populate the boot allocator Julien Grall
2022-05-23  7:28   ` Michal Orzel
2022-05-23 19:51     ` Julien Grall
2022-05-24  6:12       ` Michal Orzel
2022-05-24  7:57   ` Bertrand Marquis
2022-06-03 23:09   ` Stefano Stabellini
2022-05-20 12:09 ` [PATCH 14/16] xen/arm64: mm: Add memory to the boot allocator first Julien Grall
2022-05-26 17:10   ` Luca Fancellu
2022-06-03 23:09   ` Stefano Stabellini
2022-05-20 12:09 ` [PATCH 15/16] xen/arm: mm: Rework setup_xenheap_mappings() Julien Grall
2022-05-20 12:09 ` [PATCH 16/16] xen/arm: mm: Re-implement setup_frame_table_mappings() with map_pages_to_xen() Julien Grall
2022-05-26 17:24   ` Luca Fancellu
2022-06-03 23:09   ` Stefano Stabellini
2022-06-08  1:14   ` Stefano Stabellini
2022-06-11 11:30 ` [PATCH 00/16] xen/arm: mm: Remove open-coding mappings Julien Grall

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