linux-kernel - Re: [PATCH v3 3/4] tpm: add SNP SVSM vTPM driver

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Message-ID: <imld77cuc6e4kyd5an5oeerfseit3l4enrbpazne2ybo34srik@ejqwayyod2mv>
Date: Thu, 20 Mar 2025 12:18:35 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Tom Lendacky <thomas.lendacky@....com>, 
	Jarkko Sakkinen <jarkko@...nel.org>, Peter Huewe <peterhuewe@....de>, x86@...nel.org, 
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>, linux-integrity@...r.kernel.org, 
	Dov Murik <dovmurik@...ux.ibm.com>, Dionna Glaze <dionnaglaze@...gle.com>, 
	linux-coco@...ts.linux.dev, James Bottomley <James.Bottomley@...senpartnership.com>, 
	Claudio Carvalho <cclaudio@...ux.ibm.com>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH v3 3/4] tpm: add SNP SVSM vTPM driver

On Wed, Mar 19, 2025 at 08:44:22PM -0300, Jason Gunthorpe wrote:
>On Tue, Mar 18, 2025 at 05:18:53PM +0100, Stefano Garzarella wrote:
>
>> I see, thanks for the clarification!
>> I saw that with devm_get_free_pages() I can easily allocate a
>> resource-managed page, so I'll do that in v4.
>
>As a general note you should just use kmalloc these days, even for
>PAGE_SIZE. It is efficient and OK.

Thanks for sharing!

I think I'll stay with devm_get_free_pages() just because if it's
page aligned (with kmalloc I'm not sure if I have a way to ensure it), 
it can be a bitter faster for SVSM to map/unmap it on every command.

>
>Having a struct that is PAGE_SIZE+1 is not efficient and will waste
>a page of memory. That should be avoided ..

Got it, I will definitely split the buffer allocation from the priv.

Thanks,
Stefano