Re: [Qemu-devel] [PATCH v2 for-2.0] target-i386: x86_cpu_get_phys_page_debug(): support 1GB page translation

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2014-03-19 22:03, Luiz Capitulino wrote:
> Linux guests, when using more than 4GB of RAM, may end up using 1GB pages
> to store (kernel) data. When this happens, we're unable to debug a running
> Linux kernel with GDB:
> 
> (gdb) p node_data[0]->node_id
> Cannot access memory at address 0xffff88013fffd3a0
> (gdb)
> 
> GDB returns this error because x86_cpu_get_phys_page_debug() doesn't support
> translating 1GB pages in IA-32e paging mode and returns an error to GDB.
> 
> This commit adds support for 1GB page translation for IA32e paging.
> 
> Signed-off-by: Luiz capitulino <lcapitulino@redhat.com>
> ---
> 
> - I'm proposing this patch for 2.0 because GDB debugging of large Linux
>   guests is kind of broken
> 
> - Changelog v2:
>   - Move PS bit handling to if (env->hflags & HF_LMA_MASK) block
>   - Update changelog
> 
>  target-i386/helper.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/target-i386/helper.c b/target-i386/helper.c
> index 4f447b8..7cee501 100644
> --- a/target-i386/helper.c
> +++ b/target-i386/helper.c
> @@ -941,6 +941,14 @@ hwaddr x86_cpu_get_phys_page_debug(CPUState *cs, vaddr addr)
>              pdpe = ldq_phys(cs->as, pdpe_addr);
>              if (!(pdpe & PG_PRESENT_MASK))
>                  return -1;
> +
> +            if (pdpe & PG_PSE_MASK) {
> +                page_size = 1024 * 1024 * 1024;
> +                pte = pdpe & ~( (page_size - 1) & ~0xfff);
> +                pte &= ~(PG_NX_MASK | PG_HI_USER_MASK);
> +                goto out;
> +            }
> +
>          } else
>  #endif
>          {
> @@ -993,6 +1001,7 @@ hwaddr x86_cpu_get_phys_page_debug(CPUState *cs, vaddr addr)
>          pte = pte & env->a20_mask;
>      }
>  
> +out:
>      page_offset = (addr & TARGET_PAGE_MASK) & (page_size - 1);
>      paddr = (pte & TARGET_PAGE_MASK) + page_offset;
>      return paddr;
> 

Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>

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