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Re: [PATCH 1/2] x86/ucode: allow cpu_request_microcode() to skip memory allocation
- To: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 8 Dec 2022 16:34:25 +0100
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- Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 08 Dec 2022 15:34:44 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08.12.2022 14:59, Andrew Cooper wrote:
> On 08/12/2022 13:26, Sergey Dyasli wrote:
>> @@ -240,20 +240,20 @@ static const struct microcode_patch *nmi_patch =
>> ZERO_BLOCK_PTR;
>> * patch is found and an error occurs during the parsing process. Otherwise
>> * return NULL.
>> */
>> -static struct microcode_patch *parse_blob(const char *buf, size_t len)
>> +static const struct microcode_patch *parse_blob(const char *buf, size_t len)
>> {
>> alternative_vcall(ucode_ops.collect_cpu_info);
>>
>> - return alternative_call(ucode_ops.cpu_request_microcode, buf, len);
>> + return alternative_call(ucode_ops.cpu_request_microcode, buf, len,
>> true);
>> }
>>
>> -static void microcode_free_patch(struct microcode_patch *patch)
>> +static void microcode_free_patch(const struct microcode_patch *patch)
>> {
>> - xfree(patch);
>> + xfree((void *)patch);
>
> This hunk demonstrates why the hook wants to return a non-const
> pointer. Keeping it non-const will shrink this patch quite a bit.
Alternatively it demonstrates why xfree() should take const void *,
just like e.g. unmap_domain_page() or vunmap() already do. We've
talked about this before, and the argument hasn't changed: Neither
unmapping nor freeing really alters the contents of the pointed to
area from the perspective of the caller, as the contents simply
disappears altogether.
Jan
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