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Re: [MINI-OS PATCH 1/2] mm: provide a way to do very early page table allocations
- To: Jürgen Groß <jgross@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 28 Jul 2025 17:07:18 +0200
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- Cc: samuel.thibault@xxxxxxxxxxxx, minios-devel@xxxxxxxxxxxxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 28 Jul 2025 15:15:14 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 28.07.2025 17:01, Jürgen Groß wrote:
> On 28.07.25 16:09, Jan Beulich wrote:
>> On 08.07.2025 08:37, Juergen Gross wrote:
>>> @@ -664,7 +669,16 @@ static int need_pgt_func(unsigned long va, unsigned
>>> int lvl, bool is_leaf,
>>> }
>>>
>>> pt_mfn = virt_to_mfn(pte);
>>> - pt_pfn = virt_to_pfn(alloc_page());
>>> + if ( n_early_pt )
>>> + {
>>> + n_early_pt--;
>>> + pt_addr = (unsigned long)&early_pt[n_early_pt * PAGE_SIZE];
>>> + }
>>> + else
>>> + {
>>> + pt_addr = alloc_page();
>>> + }
>>
>> The failure pattern when one fails to increase early_pt[] is likely going
>> to be problematic. Wouldn't it be better to check for failure here?
>
> Hmm, not sure this is true. I tried the shared info mapping without adding
> the special early alloc code first and finding the bug was quite easy.
Feel free to ignore my comment then.
Jan
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