[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v3 14/22] x86/boot: choose AP stack based on APIC ID
- To: Sergii Dmytruk <sergii.dmytruk@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 30 Jun 2026 09:17:59 +0200
- Authentication-results: eu.smtp.expurgate.cloud; dkim=pass header.s=google header.d=suse.com header.i="@suse.com" header.h="Content-Transfer-Encoding:In-Reply-To:Autocrypt:From:Content-Language:References:Cc:To:Subject:User-Agent:MIME-Version:Date:Message-ID"
- 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: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, trenchboot-devel@xxxxxxxxxxxxxxxx
- Delivery-date: Tue, 30 Jun 2026 07:18:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.06.2026 00:18, Sergii Dmytruk wrote:
> On Thu, Jan 22, 2026 at 04:52:36PM +0100, Jan Beulich wrote:
>>> --- a/xen/arch/x86/boot/x86_64.S
>>> +++ b/xen/arch/x86/boot/x86_64.S
>>> @@ -15,7 +15,33 @@ ENTRY(__high_start)
>>> mov $XEN_MINIMAL_CR4,%rcx
>>> mov %rcx,%cr4
>>>
>>> - mov stack_start(%rip),%rsp
>>> + test %ebx,%ebx
>>> + cmovz stack_start(%rip), %rsp
>>> + jz .L_stack_set
>>> +
>>> + /* APs only: get stack base from APIC ID saved in %esp. */
>>> + mov $-1, %rax
>>
>> Here and below 32-bit insn would do fine. However, ...
>
> Are all addresses guaraneed to be below 4 GiB?
You use %rax as the loop induction variable, so there isn't any address
in it? Plus you already use ...
>>> + lea x86_cpu_to_apicid(%rip), %rcx
>>> +1:
>>> + add $1, %rax
>>> + cmp $NR_CPUS, %eax
... as 32-bit insn here anyway.
>>> + jb 2f
>>> + hlt
>>> +2:
>>> + cmp %esp, (%rcx, %rax, 4)
>>> + jne 1b
>>
>> ... can't all of this be a simple REPNE SCASL?
>
> It can, but then can't have an upper bound, right?
I fear I don't understand the question. REPNE SCASL scans at most %rcx
slots, whatever %rcx is set to up front.
>> As to the upper bound of NR_CPUS, do we really need to look this far?
>
> Are you suggesting to use `max_cpus` instead?
Whatever the dynamically determined upper bound is, yes.
Jan
|
