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

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Message-ID: <14021d2a-2a94-a0c8-88db-acbc04b4daac@redhat.com>
Date:   Thu, 16 Mar 2017 11:48:48 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Brijesh Singh <brijesh.singh@....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
Subject: Re: [RFC PATCH v2 26/32] kvm: svm: Add support for SEV
 LAUNCH_UPDATE_DATA command



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.

> +	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.

Paolo

> +	data->handle = sev_get_handle(kvm);
> +	data->length = len;
> +	data->address = __sev_page_pa(inpages[0]) + offset;
> +	ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_DATA,
> +			data, &argp->error);
> +	if (ret)
> +		goto err_3;
> +
> +	/* update remaining pages */
> +	for (i = 1; i < nr_pages; i++) {
> +
> +		len = min_t(size_t, PAGE_SIZE, ulen);
> +		ulen -= len;
> +		data->length = len;
> +		data->address = __sev_page_pa(inpages[i]);
> +		ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_DATA,
> +					data, &argp->error);
> +		if (ret)
> +			goto err_3;
> +	}