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Re: [PATCH v1] xen/riscv: Increase XEN_VIRT_SIZE


  • To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Mon, 31 Mar 2025 18:14:03 +0200
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Mon, 31 Mar 2025 16:14:15 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 31.03.2025 17:20, Oleksii Kurochko wrote:
> A randconfig job failed with the following issue:
>   riscv64-linux-gnu-ld: Xen too large for early-boot assumptions
> 
> The reason is that enabling the UBSAN config increased the size of
> the Xen binary.
> 
> Increase XEN_VIRT_SIZE to reserve enough space, allowing both UBSAN
> and GCOV to be enabled together, with some slack for future growth.

At some point you may want to use 2M mappings for .text (rx), .rodata
(r), and .data (rw). Together with .init that would then completely
fill those 8Mb afaict. Hence you may want to go a little further right
away, e.g. to 16Mb.

> --- a/xen/arch/riscv/include/asm/mm.h
> +++ b/xen/arch/riscv/include/asm/mm.h
> @@ -43,13 +43,19 @@ static inline void *maddr_to_virt(paddr_t ma)
>   */
>  static inline unsigned long virt_to_maddr(unsigned long va)
>  {
> +    const unsigned int vpn1_shift = PAGETABLE_ORDER + PAGE_SHIFT;
> +    const unsigned long va_vpn = va >> vpn1_shift;
> +    const unsigned long xen_virt_starn_vpn =

s/starn/start/ ?

> +        _AC(XEN_VIRT_START, UL) >> vpn1_shift;
> +    const unsigned long xen_virt_end_vpn =
> +        xen_virt_starn_vpn + ((XEN_VIRT_SIZE >> vpn1_shift) - 1);
> +
>      if ((va >= DIRECTMAP_VIRT_START) &&
>          (va <= DIRECTMAP_VIRT_END))
>          return directmapoff_to_maddr(va - directmap_virt_start);
>  
> -    BUILD_BUG_ON(XEN_VIRT_SIZE != MB(2));
> -    ASSERT((va >> (PAGETABLE_ORDER + PAGE_SHIFT)) ==
> -           (_AC(XEN_VIRT_START, UL) >> (PAGETABLE_ORDER + PAGE_SHIFT)));
> +    BUILD_BUG_ON(XEN_VIRT_SIZE != MB(8));

Is it necessary to be != ? Won't > suffice?

> +    ASSERT((va_vpn >= xen_virt_starn_vpn) && (va_vpn <= xen_virt_end_vpn));

Are you sure about <= on the rhs of the && ?

> --- a/xen/arch/riscv/mm.c
> +++ b/xen/arch/riscv/mm.c
> @@ -31,20 +31,21 @@ unsigned long __ro_after_init phys_offset; /* = 
> load_start - XEN_VIRT_START */
>  #define LOAD_TO_LINK(addr) ((unsigned long)(addr) - phys_offset)
>  
>  /*
> - * It is expected that Xen won't be more then 2 MB.
> + * It is expected that Xen won't be more then 8 MB.
>   * The check in xen.lds.S guarantees that.
> - * At least 3 page tables (in case of Sv39 ) are needed to cover 2 MB.
> + * At least 6 page tables (in case of Sv39) are needed to cover 8 MB.
>   * One for each page level table with PAGE_SIZE = 4 Kb.
>   *
> - * One L0 page table can cover 2 MB(512 entries of one page table * 
> PAGE_SIZE).
> + * Four L0 page table can cover 8 MB(512 entries of
> + * one page table * PAGE_SIZE).
>   *
>   * It might be needed one more page table in case when Xen load address
>   * isn't 2 MB aligned.
>   *
> - * CONFIG_PAGING_LEVELS page tables are needed for the identity mapping,
> + * (CONFIG_PAGING_LEVELS + 2) page tables are needed for the identity 
> mapping,
>   * except that the root page table is shared with the initial mapping
>   */
> -#define PGTBL_INITIAL_COUNT ((CONFIG_PAGING_LEVELS - 1) * 2 + 1)
> +#define PGTBL_INITIAL_COUNT ((CONFIG_PAGING_LEVELS + 2) * 2 + 1)

I'm in trouble fitting the comment updates with the update of the #define. Why
would more tables be needed for the identity mapping? Why does XEN_VIRT_SIZE
not appear anywhere here?

Jan



 


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