linux-kernel - Re: [RFC PATCH v2 26/32] kvm: svm: Add support for SEV LAUNCH_UPDATE

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Date:   Thu, 16 Mar 2017 13:20:06 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>, <simon.guinot@...uanux.org>,
        <linux-efi@...r.kernel.org>, <kvm@...r.kernel.org>,
        <rkrcmar@...hat.com>, <matt@...eblueprint.co.uk>,
        <linux-pci@...r.kernel.org>, <linus.walleij@...aro.org>,
        <gary.hook@....com>, <linux-mm@...ck.org>,
        <paul.gortmaker@...driver.com>, <hpa@...or.com>, <cl@...ux.com>,
        <dan.j.williams@...el.com>, <aarcange@...hat.com>,
        <sfr@...b.auug.org.au>, <andriy.shevchenko@...ux.intel.com>,
        <herbert@...dor.apana.org.au>, <bhe@...hat.com>,
        <xemul@...allels.com>, <joro@...tes.org>, <x86@...nel.org>,
        <peterz@...radead.org>, <piotr.luc@...el.com>, <mingo@...hat.com>,
        <msalter@...hat.com>, <ross.zwisler@...ux.intel.com>, <bp@...e.de>,
        <dyoung@...hat.com>, <thomas.lendacky@....com>, <jroedel@...e.de>,
        <keescook@...omium.org>, <arnd@...db.de>, <toshi.kani@....com>,
        <mathieu.desnoyers@...icios.com>, <luto@...nel.org>,
        <devel@...uxdriverproject.org>, <bhelgaas@...gle.com>,
        <tglx@...utronix.de>, <mchehab@...nel.org>,
        <iamjoonsoo.kim@....com>, <labbott@...oraproject.org>,
        <tony.luck@...el.com>, <alexandre.bounine@....com>,
        <kuleshovmail@...il.com>, <linux-kernel@...r.kernel.org>,
        <mcgrof@...nel.org>, <mst@...hat.com>,
        <linux-crypto@...r.kernel.org>, <tj@...nel.org>,
        <akpm@...ux-foundation.org>, <davem@...emloft.net>
CC:     <brijesh.singh@....com>
Subject: Re: [RFC PATCH v2 26/32] kvm: svm: Add support for SEV
 LAUNCH_UPDATE_DATA command


On 03/16/2017 05:48 AM, Paolo Bonzini wrote:
>
>
> On 02/03/2017 16:17, Brijesh Singh wrote:
>> +static struct page **sev_pin_memory(unsigned long uaddr, unsigned long ulen,
>> +				    unsigned long *n)
>> +{
>> +	struct page **pages;
>> +	int first, last;
>> +	unsigned long npages, pinned;
>> +
>> +	/* Get number of pages */
>> +	first = (uaddr & PAGE_MASK) >> PAGE_SHIFT;
>> +	last = ((uaddr + ulen - 1) & PAGE_MASK) >> PAGE_SHIFT;
>> +	npages = (last - first + 1);
>> +
>> +	pages = kzalloc(npages * sizeof(struct page *), GFP_KERNEL);
>> +	if (!pages)
>> +		return NULL;
>> +
>> +	/* pin the user virtual address */
>> +	down_read(&current->mm->mmap_sem);
>> +	pinned = get_user_pages_fast(uaddr, npages, 1, pages);
>> +	up_read(&current->mm->mmap_sem);
>
> get_user_pages_fast, like get_user_pages_unlocked, must be called
> without mmap_sem held.

Sure.

>
>> +	if (pinned != npages) {
>> +		printk(KERN_ERR "SEV: failed to pin  %ld pages (got %ld)\n",
>> +				npages, pinned);
>> +		goto err;
>> +	}
>> +
>> +	*n = npages;
>> +	return pages;
>> +err:
>> +	if (pinned > 0)
>> +		release_pages(pages, pinned, 0);
>> +	kfree(pages);
>> +
>> +	return NULL;
>> +}
>>
>> +	/* the array of pages returned by get_user_pages() is a page-aligned
>> +	 * memory. Since the user buffer is probably not page-aligned, we need
>> +	 * to calculate the offset within a page for first update entry.
>> +	 */
>> +	offset = uaddr & (PAGE_SIZE - 1);
>> +	len = min_t(size_t, (PAGE_SIZE - offset), ulen);
>> +	ulen -= len;
>> +
>> +	/* update first page -
>> +	 * special care need to be taken for the first page because we might
>> +	 * be dealing with offset within the page
>> +	 */
>
> No need to special case the first page; just set "offset = 0" inside the
> loop after the first iteration.
>

Will do.

-Brijesh